| Títol | Conferenciant | Procedència | Data | Resum |
|---|
| The Role of Viscosity in Galaxy Clusters | Tirso Marín-Gilabert | Universitäts-Sternwarte München/Ludwig-Maximilians-Universität, Alemanya | 2023-09-14 | The evolution of galaxy clusters is highly influenced by the dynamics of the Intracluster Medium (ICM), which govern crucial aspects such as mixing, turbulence processes, and galaxy interactions within the cluster environment. Among the factors influencing the ICM dynamics, the impact of viscosity is still under debate. Understanding the effect of viscosity on the evolution of galaxy clusters is fundamental for comprehending gas properties and the underlying dynamics within the ICM.By conducting a thorough study, we aim to highlight the implications that viscosity introduces compared to inviscid simulations. These implications encompass morphological differences, shock propagation mechanisms, and the intricate interplay with dynamo amplification, among other fundamental effects. The results of this research are expected to enhance our understanding of ICM dynamics and contribute to our knowledge of galaxy cluster evolution. |
| Interpreting solar observations with deep learning | Ignasi Soler Poquet | Rosseland Centre for Solar Physics (RoCS), University of Oslo, Noruega | 2023-06-27 | |
| Compactified Hyperboloidal Evolution in Numerical Relativity | Shalabh Gautam | ICTS, Bengaluru, Índia | 2023-06-21 | One symmetric hyperbolic formulation of the Einstein Field Equations (EFEs) is in generalized harmonic gauge. The choice of gauge is generally related to the coordinates used to cast the EFEs within a spacetime foliation. A naive choice of gauge adapted to hyperboloidal coordinates may not be the most optimal way to solve the EFEs on these slices. In this talk, we shall discuss a choice of compactified hyperboloidal coordinates that not only are physically motivated but also facilitate mapping future-null infinity onto a finite computational grid. We decouple our choice of gauge from this choice of coordinates to maintain the hyperbolicity of the EFEs via the dual-foliation formalism. We introduce a numerical scheme that assures stability for a class of linear hyperbolic systems on these slices. Finally, we discuss the possibility of extending this numerical scheme for studying initial value problems for the EFEs on these slices. |
| Applications of conformal geometry in general relativity | Alfonso García Parrado | Universidad de Córdoba | 2023-05-30 | Some of the most relevant applications of conformal geometry in general relativity will be reviewed. We will discuss Penrose diagrams, Friedrich Conformal field equations, conformal Killing vector fields, and conformally invariant differential operators. |
| Caracterització IDEAL d'espai-temps | Joan Ferrando | Departament d'Astronomia i Astrofísica, Universitat de València | 2023-05-16 | Des dels inicis de la geometria Riemanniana l'estudi de les propietats invariants de les mètriques i la seua caracterizació invariant han estat temes que s'han tractat àmplament i des de diversos punts de vista. En aquesta xerrada es donaran algunes nocions sobre el tema, i es presentaran algunes caracteritzacions de camps gravitatoris obtingudes pel grup de Gravitació i Posicionament Relativista del nostre departament. |
| Stability and physical properties of spherical excited scalar boson stars | Marco Brito | Universidade de Aveiro, Portugal | 2023-03-28 | We study the time evolution of spherical, excited - with n radial nodes - scalar boson stars in General Relativity minimally coupled to a complex massive scalar field with quartic self-interactions. We report that these stars, with up to n=10, can be made dynamically stable, up to timescales of t~10^4/(c mu), where mu is the inverse Compton wavelength of the scalar particle, for sufficiently large values of the self-interactions coupling constant lambda, which depend on n. We observe that the compactness of these solutions is rather insensitive to n, for large lambda and fixed frequency. Generically, along the branches where stability was studied, these excited boson stars are not compact enough to allow for ISCOs or light rings. Finally, we discuss the angular velocity of particles along timelike circular orbits, suggesting an application, for solutions in the Newtonian limit, to galactic rotation curves. |
| Observing Sagittarius A* with ALMA | Maciek Wielgus | Max-Planck-Institut für Radioastronomie, Bonn, Alemanya | 2023-03-14 | Sagittarius A* is a supermassive black hole in the center of the Milky Way. With the exquisite sensitivity of ALMA we can study the event horizon-scale variability of this system with unprecedented time cadence and signal to noise ratio. I will present the recent findings of the full-Stokes Sagittarius A* light curve analysis and their relation to the observations by the Event Horizon Telescope. I will also discuss the results of the orbital motion model application to the Sagittarius A* linear polarization ALMA light curves at millimeter wavelength, and the emerging theoretical connection to the high energy flaring activity of the system. |
| Numerical construction of non-linear initial data sets for cosmological models | Alejandro Estrada | Universidad del Valle, Colòmbia | 2023-03-07 | |
| On the development of discontinuous Galerkin methods for neutrino radiation hydrodynamics | Eirik Endeve | Oak Ridge National Laboratory, USA | 2023-03-06 | Simulations of core-collapse supernovae (CCSNe) and other systems of interest in nuclear astrophysics call for the use of a relativistic model. Currently, several groups are tackling this computational challenge with algorithms based on finite volume or finite difference methods. More recently, discontinuous Galerkin (DG) methods have gained increased attention in the computational astrophysics community, in part due to their scalability, but they have yet to be applied to model CCSNe. In this seminar I will discuss our efforts to develop DG methods for relativistic neutrino radiation hydrodynamics and their implementation in the toolkit for high-order neutrino radiation hydrodynamics (thornado), which are based on solving a spectral two-moment model with algebraic closure. I will first introduce the two-moment model, the discretization in phase-space with DG methods and time integration with implicit-explicit methods. Then I will provide details on our strategy for solving the nonlinear system modeling the coupling between neutrinos and matter. I will end with some preliminary numerical results demonstrating the performance of the methods in idealized settings. |
| Simulating transient noise burst in LIGO: gengli and its applications | Melissa López | Universitat d'Utrecht, Països Baixos | 2023-03-02 | The noise of gravitational-wave (GW) interferometers limits their sensitivity and impacts the data quality, hindering the detection of GW signals from astrophysical sources. For transient searches, the most problematic are transient noise artefacts, known as glitches, that happens at a rate around 1/min, and can mimic GW signals. Because of this, there is a need for better modelling and inclusion of glitches in large-scale studies, such as stress testing the pipelines. In this proof-of-concept work, we employ Generative Adversarial Networks (GAN), a state-of-the-art Deep Learning algorithm inspired by Game Theory, to learn the underlying distribution of blip glitches and to generate artificial populations. We reconstruct the glitch in the time domain, providing a smooth input that the GAN can learn. We share the trained network through a user-friendly open-source software package called gengli and provide practical examples of its usage. |
| Gravitational-wave detectors in the next decade | Matteo Barsuglia | Université de Paris, CNRS, Astroparticule et Cosmologie, França | 2023-02-28 | After the first gravitational wave detection in 2015 and the multi-messenger observation of the binary neutron stars merger in 2017, gravitational wave astronomy has evolved rapidly. In 2019-2020, LIGO-Virgo carried out its third observing campaign, reaching nearly a hundred sources. Over the next decade, the gravitational wave detector network (which includes the 2 LIGOs, Virgo and Japanese KAGRA) will alternate between data takings and improvements. After recalling the scientific results obtained with previous observations, in this seminar I will discuss the main ideas and plans to improve interferometric gravitational wave detectors in the next decades and the scientific potential enabled by these improvements. In particular, I will describe how to circumvent the limitations imposed by quantum mechanics on detector sensitivity, such as the injection of “squeezed” vacuum states. |
| The filamentary internal structure of the 3C279 blazar jet | Teresa Toscano | Instituto de Astrofísica de Andalucía (IAA-CSIC) | 2023-02-14 | Supermassive black holes at the centre of active galactic nuclei power some of the most luminous objects in the Universe. Typically, VLBI observations of blazars have revealed little information of the ejected plasma internal structure. We show extremely-high angular resolution images of the blazar 3C 279 obtained with the space VLBI mission RadioAstron in 2014, which allowed us to resolve the jet transversely and reveal several filaments produced by Kelvin-Helmholtz instabilities in a kinetically dominated flow that originate from the core and extend up to 175 parsecs (de-projected) downstream the jet. From the observed linear polarization and strong cross-section emission asymmetry we can infer that the filaments are threaded by a helical magnetic field rotating clockwise in the direction of the flow motion. In the same line, we have now 2018 data of the same source, also with RadioAstron, so we can see whether the source has changed and how, both in shape and polarization. |
| The high-energy collision of charged black holes | Gabriele Bozzola | Universitat d'Arizona, USA | 2023-01-17 | Ultra-relativistic collisions of black holes are ideal settings where to investigate how general relativity behaves under extreme conditions. A large fraction of the allowed parameter space has been explored over the past 13 years (including mass, spin, impact parameter), with the notable exception of charge. The inclusion of charge is significant because it adds non trivial degrees of freedom to the system. For example, charge constitutes another way to reach extremality (together with spin) and opens up a new channel to radiate away energy (through electromagnetic waves). Moreover, charge makes the study more directly relevant to particle physics and the production of microscopic black holes in cosmic rays and in particle accelerators. In this talk, I am going to present the first numerical-relativity simulations of head-on collisions of black holes with the same charge and mass. In particular, I am going to discuss what they can teach us about a variety of conjectures, including cosmic censorship and the role of the inner structure of bodies colliding at relativistic speed. |
| Exoplanetas jóvenes: técnicas para descubrir estos objetos escurridizos | Carlos del Burgo Díaz | Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE), Mèxic | 2022-12-15 | Además del Sol, la mayor parte de estrellas de la Vía Láctea albergan planetas, los llamados planetas extrasolares o exoplanetas. Aproximadamente un dos por ciento de las estrellas son jóvenes. En su juventud las estrellas son particularmente activas, lo que dificulta el descubrimiento de los planetas que las circundan. El reto estriba en que, en las series temporales obtenidas con el método Doppler y el de tránsito (las más recurridas hasta la fecha), la señal del planeta es típicamente una décima parte o menos de la que corresponde a la actividad estelar. Los estudios en detalle son laboriosos a la vez que fascinantes y aún está pendiente la escritura de los libros de texto. En este seminario presentaré los exoplanetas más jóvenes que hemos descubierto hasta ahora y las dificultades en la interpretación de sus propiedades a partir de los modelos teóricos existentes de formación y evolución planetaria. |
| La tensión cosmológica desaparece con una revisión del concepto de masa gravitatoria | Miquel Portilla | Departament d'Astronomia i Astrofísica, Universitat de València | 2022-10-13 | La discrepancia entre los valores de la constante de Hubble obtenidos analizando la radiación de fondo de microondas del universo primitivo: Ho = 67.4 ± 0.5 Km seg-1 Mpc-1, (Planck Results 2018), y el obtenido considerando supernovas en épocas recientes: Ho = 73.5 ± 1.4 Km seg-1 Mpc-1, (A. G. Riess 2019) puede explicarse como consecuencia de una revisión del concepto de masa gravitatoria en Relatividad General propuesta recientemente (M. Portilla 2022). |
| Universal relations for rotating Boson Stars | Jorge Castelo | Universidade de Santiago de Compostela | 2022-10-06 | Boson stars are hypothetical but widely considered exotic compact objects known as ``black-hole mimickers” whose mergers may produce gravitational-wave emissions observable by current ground-based detectors like Advanced LIGO and Virgo. We need ways to tell different types of compact bodies apart, and universal relations are excellent tools for this purpose since they allow us to know the external gravitational field of particular types of compact stars. Therefore, having universal relations for rotating boson stars would help us to identify these objects and lift possible degeneracies with other compact stars. We show that the moment of inertia I, the (dimensionless) angular momentum χ, and the quadrupole moment Q of rotating boson stars obey a universal relation, valid for a wide set of boson-star models. Further, the obtained I-χ-Q relation clearly differs from its famous neutron star counterpart. In GW observations, this provides an unequivocal diagnostic tool to distinguish boson stars from ordinary compact stars or other celestial bodies. Such universal (i.e. model-independent) relations also provide a valuable tool to probe the strong gravity regime of general relativity and to constrain the equation of state of matter inside compact stars. |
| Chemical abundances of time-series spectra of Classical Cepheids with WINERED | Scarlet S. Elgueta | Tokio University, Japó | 2022-07-25 | Classical Cepheids have been proved to be multipurpose, their use is not only limited to precise distance determinations, they are excellent chemical tracers as their spectra exhibit a large number of absorption lines of various kinds of elements. Moreover, the analysis of the spectra collected by the high-resolution near-infrared spectrograph WINERED in the Y-J bands has revealed a robust number of newly identified absorption lines corresponding to Fe-peak, alpha-enhanced, heavy metallic, and biogenic elements. Here, I plan to review the methodology applied in my doctoral thesis that led to precise and accurate measurements of fundamental stellar parameters of the sample of Cepheids under analysis, which, in tandem, led to abundance estimates that are in perfect agreement with the results of long history optical studies. Thus, proving the capabilities of the unexplored YJ bands to unveil exotic regions within our galaxy, and therefore, pave the way to provide more insights into galactic archaeology through the study of different phenomena, such as the metallicity gradient of our galaxy, as well as the abundances of neutron-capture elements. |
| A follow-up of the 4C 38.41 innermost jet: Origins and evolution of its emission | Juan Carlos Algaba | University of Malaya | 2022-07-07 | Active Galactic Nuclei (AGNi) are one of the most energetic phenomena in the universe, thought to be powered by a central super massive black hole (SMBH). Most of them emit synchrotron radiation from radio to gamma rays, and indeed, most of the gamma ray sources are AGN. However, due to limited resolution, we do not know where the radiation originates. The story is very different in radio VLBI observations, where we can resolve jets and their morphology and evolution. Here we present multi-frequency simultaneous radio observations of the flat spectrum radio quasar 4C 38.41 combined with additional observations in the radio, optical, X-rays, and gamma-rays carried out during the period 2012 March-2015 August. By examining a series of multi-band flares and their correlation with ejected VLBI components, we estimate that the flares appear to be associated with new components in the source originating within a particle-dominated region. Jet components in this source follow the shock-in-jet model and evolve through a semi-parabolic jet where the magnetic field and electron densities are found to fall along the jet as $Bpropto r^{-1.5}$ and $npropto r^{-1.1}$ respectively, suggesting that the magnetic configuration upstream the jet may be dominated by the poloidal component. However, as the jet evolves towards larger scales, the polarization properties are still unclear and their study may unveil more mysteries on the dynamics of this source. |
| Implementation of advanced Riemann solvers in a numerical-relativity neutrino radiation magnetohydrodynamics code and its application to mass ejection | Kenta Kiuchi | Albert Einstein Institute, Golm, Alemanya | 2022-06-16 | We implement advanced Riemann solvers HLLC and HLLD together with an advanced Constrained Transport scheme proposed by Gardiner and Stone. Through a series of test problems, we find our new Riemann solver is always superior to HLLE, a standard solver in the numerical relativity community. In its application, we simulate binary neutron star mergers, which have a short-lived remnant, and explored the dynamical mass eject and torus mass dependence of the mass ratio of the binary. By mapping the 3D data of the remnant generated by the new code to the axisymmetric neutrino radiation viscous hydrodynamics code, we follow the evolution of the remnant up to 2-10second. We reveal a comprehensive picture of the mass ejection from the binary neutron star mergers and discuss the possibility of the binary neutron star mergers as the r-process nucleosynthesis site. |
| Dynamics of scalarized neutron stars and black holes | Daniela Doneva | Eberhard-Karls-Universitat Tübingen, Alemanya | 2022-06-15 | In the present talk, we will discuss the dynamics of spontaneous scalarization of black holes and neutron stars in extended scalar-tensor theories of gravity. We will focus on two particularly interesting nonlinear and highly dynamical scenarios for (de)scalarization - binary black hole merger and stellar core collapse. We will consider as well the gravitational phase transition that can occur for scalarized neutron stars mimicking the nuclear matter phase transition from confined hadronic to deconfined quark matter. For all these cases we will discuss the gravitational wave and electromagnetic signatures as a smoking gun of the (de)scalarization. |
| Magnetar eruptions and electromagnetic fireworks | Jens Mahlmann | Princeton University, USA | 2022-06-10 | |
| Nucleosynthesis, kilonovae, and gamma-ray bursts from neutron star mergers | Oliver Just | GSI, Darmstadt, Alemanya | 2022-05-20 | |
| Trying to reconcile the gravitational wave GW190521 and its proposed electromagnetic counterpart | Juan Calderón-Bustillo | IGFAE, Santiago de Compostela | 2022-04-08 | |
| Insight on the jet-disk connection in radio galaxies | Luca Ricci | Max-Planck-Institute for Radio Astronomy, Bonn, Alemanya | 2022-04-01 | |
| Universal relations in astrophysics | Noshad Khosravi Largani | University of Wroclaw, Polònia | 2022-01-13 | |
| Basic geometric quantities and gravitational energy | José M. M. Senovilla | Departamento de Física, Universidad del País Vasco (UPV/EHU) | 2021-10-14 | Gravity manifests itself as curvature of spacetime. Its strength can be measured by considering variations of the elementary geometric quantities (area, volume, radius) of small balls with respect to their counterparts in flat spacetime. These variations are directly related, via the Einstein field equations, to the energy density of matter at the ball's centre. In this talk I consider the case when the matter energy density vanishes. The basic geometric quantities still feel the effect of pure gravity, and the resulting changes could still be related to the gravitational strength or, in simple words, to the gravitational energy density. This leads to a novel prescription for an aproximats quasi-local energy of the pure gravitational field. |
| Stability of hypermassive neutron stars against a prompt collapse | Pawel Szewczyk | Astronomical Observatory Warsaw University, Polònia | 2021-09-23 | |
| Using numerical relativity simulations to inform gravitational self-force methods | Sergi Navarro Albalat | Physics Department, University of Texas, USA | 2020-12-16 | Numerical relativity simulations are the tool we have to solve the merger of two black holes of intermediate mass ratios in the regime of strong gravitational field, where analytic approximations fail. Interpreting the data from the simulations in the form of gravitational waves, and using it to create a waveform data base is crucial if we want to cross compare with the experimentally observed gravitational waves by LIGO-Virgo (and LISA in the coming future). More accurate waveforms translate into a more accurate determination of the astrophysical parameters of the binary black hole system. Something that hasn't been explored yet is to what extent the self-force analytic approximation, based on an expansion of the gravitational field in integer powers of the extreme mass ratio, generates accurate waveforms as we move towards the less adiabatic phases of the inspiral (for example, closer to the merger of the black holes, in the so called transition region). Understanding the limitations of this methods is necessary if we want to construct waveforms that can accurately describe the adiabatic inspiral, transition and plunge phases of the binary. Evidence has shown that the self-force approximation works well even for intermediate mass ratios (when comparing with NR simulations) during the early inspiral, but this agreement starts to fail as the black holes separation approaches the innermost stable circular orbit. Whether we can overcome this discrepancy with a different approximation will be useful to construct more accurate models. I will talk in more detail about this topic and give an update on our progress. |
| Light in the dark: GW190521 as a Proca star merger | Nicolás Sanchis Gual | Center for Astrophysics and Gravitation, Universidade de Lisboa, Portugal | 2020-12-02 | The detections of gravitational waves are opening a new window to the Universe. The nature of black holes and neutron stars may now be unveiled, but gravitational radiation may also lead to exciting discoveries of new exotic compact objects, oblivious to electromagnetic waves. In particular, Advanced LIGO-Virgo recently reported a short gravitational-wave signal (GW190521) interpreted as a quasi-circular merger of black holes, one at least populating the pair-instability supernova gap. We found that GW190521 is also consistent with numerically simulated signals from head-on collisions of two (equal mass and spin) horizonless vector boson stars (aka Proca stars). This provides the first demonstration of close degeneracy between these two theoretical models, for a real gravitational-wave event. |
| Geometric properties of Keplerian self-gravitating perfect-fluid tori around black holes | Patryk Mach | Universitat Jaguelònica, Cracòvia (Polònia) | 2020-02-18 | I will report recent results in modeling of self-gravitating perfect-fluid Keplerian tori around black holes. The emphasis will be put on geometric properties of the corresponding spacetimes and their connection with parametric bifurcation occurring in the solution space. I will discuss the nonmonotonicity of the circumferential radius and the breaking of the Pappus-Guldinus rule. If time permits, I should also comment on the occurrence of toroidal ergoregions and the properties of geodesics in the obtained spacetimes. |
| Non-linear dynamics of spinning bosonic stars: formation and stability | Nicolás Sanchis Gual | Center for Astrophysics and Gravitation, Universidade de Lisboa, Portugal | 2019-11-05 | Spherical boson and Proca stars have been extensively studied in the non-linear regime, but no numerical simulations of rotating bosonic stars have been performed. We present the first fully non-linear numerical evolutions of the fully non-linear Einstein-(complex, massive) Klein-Gordon and Einstein-(complex) Proca systems, to assess the formation and stability of spinning bosonic stars. In the formation scenario, starting with constraint-obeying initial data, describing a dilute, axisymmetric cloud of spinning scalar/Proca field, gravitational collapse towards a spinning star occurs, via gravitational cooling. In the scalar case the formation is transient a non-axisymmetric instability always develops ejecting all the angular momentum from the scalar star. In the Proca case, by contrast, no instability is observed and the evolutions are compatible with the formation of a spinning Proca star. Secondly, we address the stability of an existing star, a stationary solution of the field equations. In the scalar case, a non-axisymmetric perturbation develops collapsing the star to a spinning black hole. No such instability is found in the Proca case, where the star survives large amplitude perturbations. Our analysis suggests bosonic stars have different stability properties in the scalar/vector case, which we tentatively relate to their toroidal/spheroidal morphology. |
| Ultracompact Schwarzschild stars as black-hole 'mimickers' | Camilo Posada | Institute of Physics, Research Centre of Theoretical Physics and Astrophysics, Silesian University in Opava, República Txeca | 2019-10-31 | Exotic compact objects (ECOs), or black-hole 'mimickers', have been under scrutiny after the event GW150914. One of these ECOs is the gravastar proposed back in 2001 by Mazur and Mottola. In this talk I will review the recently discovered connection between the constant-density interior Schwarzschild solution, or 'Schwarzschild star', and gravastars. I will discuss the extension of this model to slow rotation, and also some recent investigations which suggest that Schwarzschild stars are stable against radial and non-radial perturbations, making them very good candidates as black-hole 'mimickers'. |
| Testing jet formation in a larger sample of radio galaxies | Bia Boccardi | Max-Planck-Institut für Radioastronomie, Bonn, Alemanya | 2019-10-25 | In the recent years, radio galaxies proved to be the ideal targets for studies aimed at investigating the launching mechanism of relativistic jets. Inferring the intrinsic properties of the jet base through high-resolution radio observations is easier in misaligned objects than in blazars, due to the reduced impact of Doppler boosting and projection effects. So far, very-long-baseline interferometry studies of jet formation have been performed in selected nearby objects (mainly in M87, Cygnus A, and 3C84), and have provided important observational evidence in support of the magnetic launching models. In this talk, I will discuss the attempt to identify a larger sample of radio galaxies suited for such analyses, and I will present first results concerning the high-energy emission, the collimation properties, and the internal structure of the plasma flow in still unexplored sources down to scales of hundreds Schwarzschild radii. |
| Higher order waves in (relativistic) MHD | Dr. Tomasz Rembiasz | Universitat Jaguelònica, Cracòvia (Polònia) | 2019-07-26 | I will talk about our findings in simulations of linear waves in (R)MHD, which inevitably trigger higher order waves, which trigger even higher oder waves. Some of them are amplified, some of them are damped with time because of physical and numerical reasons. The prelimiary conclusions of our findings show that without a proper characterization of these non-linear effects, further analysis of linear modes and its saturation might be inadequate. |
| Bosones ultra-ligeros como materia oscura: historía de tres potenciales escalares | Luis A. Ureña | Grupo de Gravitación y Física Matemática, Universidad de Guanajuato (campus de León), México | 2019-07-23 | El modelo de bosones ultra-ligeros para conformar la materia oscura del Universo ha estado bajo fuerte escrutinio en las últimas dos décadas, por lo que se ha convertido en un modelo de referencia alternativo al de la materia oscura fría del modelo estándar cosmológico. En esta plática presentaremos los resultados generales del modelo y las observaciones que pueden acotar sus parámetros físicos. Para ello, también exploraremos tres tipos de potenciales escalares: el cuadrático, el trigonométrico y el hiperbólico. Para estos dos últimos, además de la masa del bosón, también se considera un parámetro de auto-interacción que influye a su vez en las observables cosmológicas. Los resultados se explicarán en base a un formalismo matemático que nos permite el análisis de los tres casos de manera unificada. |
| MUPPI: a subgrid star formation and feedback prescription describing the ISM and its coupling with the AGN feedback | Giuseppe Murante | Osservatorio Astronomico di Trieste, Itàlia | 2019-06-27 | I will report on our MUlti Phase Particle Integrator (MUPPI), that integrates equations describing the flow of mass and energy between a hot and cold phase of the ISM in cosmological numerical simulations, where the Giant Molecular Clouds are not resolved. We perform such an integration on-the-fly into the simulation, instead of using solutions as in Springel&Hernquist 2003. I will show some results on simulated cosmological disk galaxy, and preliminary results on the coupling of the AGN energy feedback to the different phases of ISM gas. |
| A toy model of viscous relativistic thick disk in Schwarzschild spacetime | Sayantani Lahiri | Center of Applied Space Technology and Microgravity (ZARM), Universität Bremen, Alemanya | 2019-02-28 | The aim of the work is to explore cumulative effects of the black hole curvature and the shear viscosity on a relativistic thick accretion disk. As an initial step towards this direction, we investigate how they cast their imprints and hence influence the fluid velocity profiles of a disk which can be visualized by studying corresponding isopressure surfaces. |
| Primordial black hole formation and abundance: dependence on the shape of the inflationary power spectrum | Ilia Musco | Institut de Ciències del Cosmos, Universitat de Barcelona | 2019-02-05 | Primordial black holes can form in the early Universe from the collapse of cosmological perturbations after the cosmological horizon crossing. They are possible candidates for the dark matter as well as for the seeds of supermassive black holes observed today in the centre of galaxies. In calculations of spherically symmetric collapse, using a large curvature perturbation in the super horizon regime, the initial conditions are specified using the gradient expansion approximation in the long wave length limit. The non linear evolution is then simulated using a Lagrangian relativistic hydrodynamical code. If the perturbation is larger than a threshold depending on the equation of state and on the specific shape of the perturbation, a black hole is formed. In this talk I will discuss the dependence of PBH formation from the initial shape of the curvature profile showing the relation between the threshold amplitude and the steepness of the perturbation which is linked to the amplitude of the pressure gradients that are developing during the collapse. I will show how to derive the initial curvature profile form the shape of the inflationary power spectrum, which affects also the abundance of PBHs. Depending on the model, a proper calculation, using the shape of the power spectrum, shows that the abundance of PBHs is significantly increased by several order of magnitudes compared to previous estimations. |
| Rapidly Evolving Episodic Outflow in the Fastest Water Fountain | José María Torrelles | Institut de Ciències de l'Espai, CSIC/IEEC, Barcelona | 2019-01-08 | Water fountains (WF) are evolved stars showing early stages of collimated mass-loss during transition from the asymptotic giant branch, providing valuable insight into the formation of asymmetric planetary nebulae. In this talk, we introduce the results of our multi-epoch VLBI observations published in Orosz et al.(2019 MNRAS, 482, L45), which determine the spatial and three-dimensional kinematic structure of H2O masers associated with the fastest water fountain IRAS 18113-2503. The masers trace three pairs of high-velocity (~150-300 km/s) bipolar bow shocks on a scale of ~0.18 arcsec (~2000 au). The expansion velocities of the bow shocks exhibit an exponential decrease as a function of distance from the central star, which can be explained by an episodic, jet-driven outflow decelerating due to drag forces in a circumstellar envelope. We estimate an initial ejection velocity of ~840 km/s, and a period for the ejections of 10-20 yr, with the youngest being ~12 yr old. We hypothesize that IRAS 18113-2503 hosts a binary central star with a separation of ~10 au, revealing novel clues about the launching mechanisms of high-velocity collimated outflows in WFs. We also note that these short-lived, episodic ejections observed in the WF mimic what we also observe in some protostars. |
| The Three Hundred: A large galaxy cluster catalogue for cosmological and astrophysical applications | Weiguang Cui | Departamento de Física Teórica, Universidad Autónoma de Madrid | 2018-07-05 | Galaxy clusters are the largest gravitationally bound objects in the Universe and as such they provide a host environment for testing both cosmology models and theories of galaxy evolution. In this talk, I will introduce the 300 galaxy cluster project, which includes over 300 galaxy clusters from a MultiDark simulation. These clusters regions (radius 15Mpc/h) are resimulated by different hydro-simulation codes. Further, we also have the cluster catalogue in the same zoom-in regions from three different Semi-Analytical Models, which were run for the parent MultiDark simulation. I will also present some basic results from these catalogues. |
| Corotational and magnetorotational instabilities in relativistic thick accretion disks | Matteo Bugli | CEA Saclay - IRFU/DAp, França | 2018-06-01 | Geometrically thick tori have been widely used in the last decades to model accretion flows onto black holes. They are prone to develop a number of different instabilities, but the most important is certainly the magnetorotational instability (MRI), which triggers transport of angular momentum outwards on dynamical time-scales and the onset of MHD turbulence. However, hydrodynamic tori are also known to be unstable to the so-called Papaloizou-Pringle instability (PPI), which leads to the growth of large-scale non-axisymmetric modes that could in principle produce a detectable gravitational wave signal. Using 3D GRMHD simulations, we investigated the competition between these two instabilities considering a range of different magnetic field strengths and spectra of the initial perturbations, verifying how the action of non-axisymmetric MRI effectively suppresses the growth of the m=1 azimuthal mode selected by the PPI (although a transient growth of large-scale modes may still occur). However, relaxing the ideal MHD approximation and introducing the effects of a turbulent resistivity can inhibit the onset of the MHD turbulence, hence allowing for a significant development of the hydrodynamic instability. |
| Understanding Galaxy Clusters with Simulations | Prof. Stefano Borgani | Astronomy Unit, Dept. of Physics, University of Trieste, Itàlia | 2018-04-17 | I will overview recent advancements in the study of galaxy clusters through cosmological hydrodynamic simulations. I will discuss how improvements in the numerical description of galaxy formation processes, related to star formation and gas accretion onto super-massive black holes, is leading to the production of a realistic population of clusters from simulations. In particular I will show how the combined information from the thermo- and chemo-dynamical properties of galaxy clusters can be used as fossil records of the past history of feedback and to shed light on the cosmic cycle of baryons at different cosmic epochs. |
| Ultraviolet emission from superlumious supernovae: CSM vs. PISN vs. Magnetar | Alexey Tolstov | Senior Research Associate at the IPMU, Japó | 2018-02-23 | Observations of Gaia16apd revealed extremely luminous ultraviolet (UV) emission among superluminous supernovae (SLSNe). I will present the results of comparison of UV light curves, color temperatures, and photospheric velocities in radiation hydrodynamics simulations between the most popular SLSN models: pair-instability supernova, magnetar, and interaction with circumstellar medium. Observations at UV wavelengths can be used to clarify the nature of SLSNe and more attention should be paid to them in future follow-up observations. |
| Differentially rotating strange quark stars | Magda Szkudlarek | Universitat de Zielona Góra, Polònia | 2018-02-06 | Strange quark stars are considered as a possible alternative to neutron stars as compact objects. A hot compact star (a proto-neutron star or a strange star) born in a supernova explosion or a remnant of neutron star binary merger are expected to rotate differentially. Rotating compact stars are considered as important sources of gravitational waves for Advanced Virgo/Ligo detectors. We present results of the first relativistic calculations of differentially rotating strange quark stars for broad ranges of degree of differential rotation and maximum densities, including all previously predicted types of solutions, and compare them with results for neutrons stars. Using a highly accurate, relativistic code we show that rotation may cause a significant increase of the maximum allowed mass and can temporarily stabilize stars against prompt collapse into a black hole. |
| Core-shifts and proper-motion constraints in the S5 polar cap sample at the 15 and 43 GHz bands | Fran Abellan | Departament d'Astronomia i Astrofísica, Universitat de València | 2018-01-25 | We have studied a complete radio sample of active galactic nuclei (AGN) with the very-long-baseline-interferometry (VLBI) technique and for the first time successfully obtained high precision phase-delay astrometry at Q band (43 GHz) from observations acquired in 2010. We have compared our astrometric results with those obtained with the same technique at U band (15 GHz) from data collected in 2000. The differences in source separations among all the source pairs observed in common at the two epochs are compatible at the 1? level between U and Q bands. With the benefit of quasi-simultaneous U and Q band observations in 2010, we have studied chromatic effects (core-shift) at the radio source cores with three different methods. The magnitudes of the core-shifts are of the same order (about 0.1 mas) for all methods. However, some discrepancies arise in the orientation of the core-shifts determined through the different methods. In some cases these discrepancies are due to insufficient signal for the method used. In others, the discrepancies reflect assumptions of the methods and could be explained by curvatures in the jets and departures from conical jets. |
| Gamma-ray emission and mass-loading from stellar populations interacting with an extragalactic jet | Núria Torres Albà | Universitat de Barcelona | 2018-01-24 | Galaxies hosting an active galactic nucleus (AGN) may present relativistic jets, which propagate through the dense medium in the inner regions and interact with dense molecular clouds, young stars or even stellar clusters. In particular, we focus on the presence of whole populations of stars with strong winds entering into the jet, carrying external material which has accumulated around them, and which is peeled away when in contact with the jet pressure. The stars then further inject mass through their own stellar winds, during the full duration of their jet-crossing time. This interaction can lead to the formation of shocks in which particles can be accelerated up to relativistic energies, producing detectable high-energy non-thermal emission, as well as having dynamical effects on the jet, possibly leading to its deceleration. |
| Very deep inside the SN 1987A core ejecta: Molecular structures seen in 3D | Fran Abellan | Departament d'Astronomia i Astrofísica, Universitat de València | 2018-01-18 | Most massive stars end their lives in core-collapse supernova explosions and enrich the interstellar medium with explosively nucleosynthesized elements. Following core collapse, the explosion is subject to instabilities as the shock propagates outward through the progenitor star. Observations of the composition and structure of the innermost regions of a core-collapse supernova provide a direct probe of the instabilities and nucleosynthetic products. SN 1987A in the Large Magellanic Cloud is one of very few supernovae for which the inner ejecta can be spatially resolved but are not yet strongly affected by interaction with the surroundings. Our observations of SN1987A with the Atacama Large Millimeter/submillimeter Array are of the highest resolution to date and reveal the detailed morphology of cold molecular gas in the innermost regions of the remnant. The 3D distributions of carbon and silicon monoxide (CO and SiO) emission differ, but both have a central deficit, or torus-like distribution, possibly a result of radioactive heating during the first weeks ("nickel heating"). The size scales of the clumpy distribution are compared quantitatively to models, demonstrating how progenitor and explosion physics can be constrained. |
| Traces of magnetogenesis in large scale structures | Franco Vazza | Dipartimento di Fisica e Astronomia, Università di Bologna, Itàlia | 2017-11-09 | On large scales cosmic matter is distributed in a web consistent of clusters, filaments, walls and voids. While the dark-matter skeleton of the cosmic web is closely traced by galaxies and galaxy clusters, the large-scale gaseous distribution is more hardly detected. The warm-hot intergalactic component (T~10^5-10^7K) where nearly half of the ""missing"" cosmic baryons should be located, has yet to be firmly detected. The situation may change within the next decade, thanks to the new generation of telescopes that will soon survey the radio sky: LOFAR, MWA, Meerkat, ASKAP and the Square Kilometer Array. By detecting the radio signal from shocked cosmic web, these observations may also discover the origin of extragalactic magnetic fields. I will show how different realistic simulations of the origin of observed magnetic fields in galaxy clusters diverge in filaments and voids, and how the combination of radio observations and other high energy proxies of cosmic magnetism (including the distribution of Ultra High Energy Cosmic Rays) may help solving this fascinating and long-standing puzzle. |
| The Alleged Small-Scale Problems of LambdaCDM | Prof. Julio F. Navarro | University of Victoria, Canadà | 2017-10-26 | The Lambda Cold Dark Matter (LCDM) framework successfully accounts for observational constraints on large (> 1 Mpc) scales, from the clustering of galaxies to the angular dependence of the Cosmic Microwave Background to the structure and matter content of galaxy clusters. On the scale of individual galaxies and, in particular, of dwarf systems much fainter than the Milky Way, a number of apparent conflicts with LCDM expectations have been reported. These have prompted the consideration of a number of radical modifications to LCDM, such as the possibility that dark matter might be ""self-interacting"", or that it might not be "cold". I will review the status of these alleged problems and will report on recent work that reevaluates the observational evidence and reexamines the role of systematic uncertainties in the comparison between observation and model predictions. In particular, I will propose a possible resolution to the "cusp vs core" problem that requires no cores (an explanation for the mass discrepancy-acceleration relation that requires no changes to the mass profile of LCDM halos) and a plausible origin for the enigmatic population of galaxies inhabiting "extremely cold" dark matter halos, such as the recently discovered Crater 2 satellite. |
| A direct primitive variable recovery scheme for conservative equations: the case of relativistic hydrodynamics | Sergio Mendoza | Instituto de Astronomia, UNAM, Mèxic | 2017-10-23 | In this talk I will describe a Primitive Variable Recovery Scheme (PVRS) to solve any system of coupled differential conservative equations in such a way that the obtained solution is the primitive variable vector and not the charge vector as is traditionally done. As an example, special Relativistic Hydrodynamics in 1D (1DRHD)examples would be presented to easily comprehend the PVRS. I will also present the convergence of the method studying the numerical errors of standard shock-tube problems of 1DRHD using the fluctuations of the numerical values with respect to exact analytic solutions. Finally, I will briefly discuss the aztekas.org project, a free GNU General Public License problem which uses a PVRS to solve conservative equations. |
| Challenging the Gamma-ray burst paradigm, from prompt to afterglow | Hendrik van Eerten | Lecturer in Computational Astrophysics, Department of Physics, University of Bath, UK | 2017-09-27 | Gamma-ray burst (GRBs), lasting seconds to minutes, are the brightest known explosions in the universe and triggered by cosmologically distant cataclysmic events. 'Long' GRBs, lasting over two seconds, result from the collapse of an ultra-massive star. 'Short' GRBs are produced by merging neutron stars and thus also of interest as potential counterparts to a gravitational wave signal. Following the prompt burst of gamma rays, for both types an afterglow signal is emitted by the decelerating directed relativistic blast waves produced by the explosion. As these narrow jets slow down and ultimately end up non-relativistic and quasi-spherical, their afterglow will peak at progressively longer wavelengths from X-rays to radio. With ever-improving instrumental capability and the increase in detailed prompt and afterglow data collected very quickly following the burst, the distinction between late prompt emission and early afterglow is becoming blurred. In this talk I will discuss how recent insights challenge the standard model and how computer simulations help us to understand relativistic blast wave dynamics of energy injection and sideways spreading of the narrow jets. |
| High resolution observations with RadioAstron of VLBI jets | Laura Vega-García | Max-Planck-Institut für Radioastronomie, Bonn, Alemanya | 2017-09-21 | Space VLBI observations with RadioAstron provide a remarkable improvement of angular resolution. The RadioAstron Key Science Program ""Structure and Physics of Compact Jets in AGN"" exploits this opportunity by detailed, multifrequency imaging of a number of selected extragalactic radio sources. In this talk, I present the results obtained from the KSP observations of the relativistic jet in the quasar 0836+710 at 1.6, 5, and 22 GHz. The space VLBI images of the jet reveal a strongly transversely resolved flow, with a wealth of structure on scales ranging from 0.2 to 150 milliarcseconds. At 22GHz, the source shows also asymmetries that need to be further investigated. The multifrequency data set can be used to study spectral morphology of the jet and obtain some physical parameters. The high resolution images of another two sources will also be presented: 1642+690, and 3C273. |
| Knottiness of X-ray jets: testing the obstacle-in-jet model | Sarka Wykes | Harvard-Smithsonian Center for Astrophysics, Cambridge, MA. USA | 2017-09-19 | Recently, it has become evident that X-ray jets are ubiquitous in low-power radio galaxies. In addition to diffuse X-ray emission, many of the jets feature compact X-ray brightness enhancements ('knots'). Their radio morphology is often similar, but not identical, to the X-ray morphology, and in some cases optical counterparts are observed as well. The issue of the knot origin(s) is yet undecided, although models exist suggesting that the knots with non-zero proper motion represent moving plasma packets while the knots without detected proper motions would originate from obstacles in the jet (stars and/or clouds) in interaction with the jet plasma flow. I will show some results from our 2D hydrodynamical simulations and analytical calculations of Centaurus A's jet interacting with winds of its internal, evolved stars, with a view to investigating the properties of shocks generated in these interactions and their match to the observed X-ray knots. The fate of the material released by the embedded stars, which is carried away by the jet at a rate of ~ 0.002 solar masses per year, will be also briefly addressed. |
| Evolution of jets driven by relativistic radiation hydrodynamics as GRBs | Francisco Rivera | Universidad Michoacana de San Nicolás de Hidalgo, Mèxic | 2017-09-14 | We carry out an analysis of three-dimensional numerical simulations of jets modeled with Relativistic Radiation Hydrodynamics (RRH), that evolve on two environments: i) a stratified surrounding medium and ii) 16TI progenitor model. We consider particular processes of interaction between the fluid and radiation, specifically, free-free, bound-free, bound-bound and electron scattering opacities. In this simulations, we assume initially, that the radiation field and matter are in local thermal equilibrium, which is broken immediately after initial time. We explore a variety of initial conditions, with different radiation energy densities and Lorentz factors of the beam, in particular, mildly and ultra-relativistic jets, together with hydrodynamical and radiation pressure dominated scenarios. Finally, we construct the luminosity Light Curves (LCs) associated with all these cases. The construction of LCs is natural in the model, because the radiation is fully coupled to the hydrodynamics equations during the evolution. |
| High order ADER schemes for a unified first order hyperbolic formulation of Newtonian continuum mechanics coupled with electro-dynamics | M. Dumbser | Laboratory of Applied Mathematics, University of Trento, Trento, Italy | 2017-07-19 | In this talk, we propose a new unified first order symmetric hyperbolic and thermodynamically compatible theory of Newtonian continuum mechanics coupled with electro-dynamics. The model is able to describe the behavior of moving elasto-plastic dielectric solids as well as viscous and inviscid fluids in the presence of electro-magnetic fields. It is actually a very peculiar feature of the proposed PDE system that viscous fluids are treated just as a special case of elasto-plastic solids. This is achieved by introducing a strain relaxation mechanism in the evolution equations of the distortion tensor A, which in the case of purely elastic solids maps the current configuration to the reference configuration. The model also contains a hyperbolic formulation of heat conduction as well as a dissipative source term in the evolution equations for the electric field given by Ohm's law. Via formal asymptotic analysis we show that in the stiff limit, the governing first order hyperbolic PDE system with relaxation source terms tends asymptotically to the well-known viscous and resistive magnetohydrodynamics (MHD) equations, and to the compressible Navier-Stokes equations in the absence of electro-magnetic fields. The present work extends the unified first order hyperbolic model of Newtonian continuum mechanics recently proposed by Peshkov and Romenski (2016) to the more general case where the continuum is coupled with electro-magnetic fields. The governing PDE system is symmetric hyperbolic and satisfies the first and second principle of thermodynamics, hence it belongs to the so-called class of symmetric hyperbolic thermodynamically compatible systems (HTC), which have been studied for the first time by Godunov in 1961 and later in a series of papers by Godunov and Romenski. An important feature of the proposed model is that the propagation speeds of all physical processes, including dissipative processes, are finite. The model is discretized using high order accurate ADER discontinuous Galerkin (DG) finite element schemes with a posteriori subcell finite volume limiters and using high order ADER-WENO finite volume schemes. We show numerical test problems that explore a rather large parameter space of the model ranging from compressible Euler and Navier-Stokes flows over ideal MHD, viscous and resistive MHD to pure electro-dynamics and moving dielectric elastic solids in a magnetic field. We will also show applications of our ADER-DG framework to the ideal and resistive relativistic MHD equations. |
| Nucleosynthesis and the accuracy of reduced nuclear reaction networks for hydrodynamical simulations | Moritz Reichert | Technische Universität Darmstadt, Alemanya | 2017-06-15 | Despite growing computational power, modern simulations of core-collapse supernovae are not fully including all physical aspects. Instead, approximations are done. The feedback of nuclear energy generation due to nuclear reactions is such an approximation and currently there is no simulation that fully includes that effect. We investigated the accuracy of different reduced nuclear reaction networks and developed a new in situ reaction network. |
| The infancy of supernova remnants: evolving a supernova into its remant in 3D | Michael Gabler | Max-Planck-Institut für Astrophysik, Garching, Alemanya | 2017-06-01 | Recently, first neutrino-driven supernova explosions have been obtained in 3D, self-consistent, first-principle simulations, these models are still not always exploding robustly and, in general, the explosions are not sufficiently energetic. To constrain the explosion mechanism, and the related uncertainties, it is thus very helpful to consider observational constraints: pulsar kicks, progenitor association and supernova remnants (SNR). Recent observations of asymmetries in the supernova ejecta of Cas A are very promising, to compare to long-term simulations of the explosion. In addition 3D observations of SN87A are becoming more constraining on the geometry of the ejected material during the explosion. In this talk I will discuss our efforts to model the late time evolution of a 3D supernova explosion, where we include the effects of beta decay, which inflates the structures rich in $^{56}$Ni. The structures we find in the simulations depend on the quantities plotted. |
| Magnetar Magnetospheres | Alexei Maté | Technische Universität München, Alemanya | 2017-05-30 | There is reason to believe that quasi-periodic oscillations observed during the decaying tail of giant bursts originate from magnetars. We investigate whether the Resonant Cyclotron Scattering model of magnetars can explain the observed spectra. In order to answer this question a Monte Carlo radiation transport code (MCMaMa) was developed by M. Gabler and P. Cerdá-Durán. The code works and was tested assuming a mildly relativistic momentum distribution of charge carriers. However, the current model cannot reproduce the observed hard X-Ray part of the spectrum up to 80 keV and there is reason to believe that the charge carriers are in fact highly relativistic. The goal of our present work is to provide an extension of the existing code MCMaMa, that calculates the momentum distribution of the charge carriers. In order to obtain a more realistic model of the particle momenta, the momentum distribution and the radiation transport have to be calculated self consistently. The more accurate description of the momentum distribution of the magnetospheric charges will provide a prediction of the hard tail component of the quiescent magnetar spectrum that can be compared to observations. |
| Kerr black holes with bosonic hair: theory and phenomenology | Carlos Herdeiro | Departamento de Física da Universidade de Aveiro, Portugal | 2017-02-02 | Over the last two years it has been found that new classes of asymptotically flat black hole solutions, regular on and outside the event horizon, bifurcating from the vacuum Kerr solution, exist in General Relativity, with simple matter contents that obey all energy conditions, namely Kerr black holes with scalar hair and Proca hair. In this talk I will review the general mechanism that allows these solutions to exist, intimately connected to superradiance, how these solutions circumvent well known no-hair theorems and some of their phenomenology (shadows and x-ray spectra) which can be considerably distinct from that of Kerr. |
| Star formation efficiencies of radio galaxies | Álvaro Labiano | Centro de Astrobiología (CSIC/INTA) | 2016-12-20 | Powerful radio galaxies show evidence of ongoing active galactic nuclei (AGN) feedback, mainly in the form of fast, massive outflows. Yet, it is not clear how these outflows affect the star formation of their hosts. It is thought that most radio galaxies will show quenched star formation, compared with the KS-law. We investigated the different manifestations of AGN feedback in two radio galaxies: the evolved 3C 293 radio source, and in the young, reactivated 3C 236. Both sources harbor young star-forming regions and fast outflows of H I and ionized gas. Due to the different evolution stages of these sources, they are expected to be at different phases of the AGN-ISM interaction process. We studied the distribution and kinematics of the molecular gas in these sources, and their star-formation properties using all available SFR tracers. Our results suggest that the apparently low efficiency of radio galaxies is not necessarily due to AGN feedback, but may be caused by an underestimation of the SFR and/or an overestimation of the molecular gas densities in the host. |
| The EAGLE project: modelling galaxy formation and evolution | Claudio Dalla Vecchia | Instituto de Astrofísica de Canarias | 2016-12-01 | I will talk about the improvements in hydrodynamical cosmological simulations and the modelling of the formation and evolution of the observed galaxy population within the EAGLE simulation project. I will show results from EAGLE and other projects using the EAGLE model. I will also describe what data has been made publicly available, and give a couple of examples on how it could be used. |
| Inversión de la ecuación de transporte radiativo | José Carlos del Toro Iniesta | Solar Physics Group, Instituto de Astrofísica de Andalucía (IAA-CSIC) | 2016-10-19 | Desde principio de los años 1970, las técnicas de inversión se han convertido en las herramientas más útiles para inferir las propiedades magnéticas, dinámicas y termodinámicas de la atmósfera solar. En la literatura han aparecido inversiones con un creciente grado de complejidad: las inferencias astrofísicas no solo dependen de las medidas, sino también de las suposiciones físicas que nos explican la formación de las líneas espectrales y de su detección con el instrumento correspondiente. Tal dependencia intrínseca en los modelos precisa una formulación específica que incluya la física supuesta de una forma cuantitativa. El núcleo de dicha física radica en la ecuación de transporte radiativo (RTE) en la que las propiedades de la atmósfera solar (estelar) se suponen conocidas y los parámetros de Stokes constituyen las incógnitas. La solución de la RTE se conoce como el problema directo. Desde un punto de vista observacional, sin embargo, el problema es el contrario: los datos conocidos son los parámetros de Stokes de la luz, mientras que las incógnitas son las magnitudes físicas solares. Invertir, pues, la ecuación de transporte radiativo es obligatorio. De hecho, la solución formal de dicha ecuación se puede considerar en sí misma como una ecuación integral. La solución de tal ecuación integral es lo que se conoce como problema inverso. Las técnicas de inversión son códigos automáticos destinados a resolver el problema inverso. En la charla comentaremos someramente las técnicas de inversión haciendo énfasis explícito en las numerosas suposiciones que subyacen. Lo más recomendable resulta seguir un grado de complejidad incremental paso a paso, en el que primero se obtiene una descripción gruesa o somera que reproduce las características principales de los perfiles de Stokes con atmósferas modelo simples. Si los perfiles de Stokes están bien muestreados y las diferencias entre observación y teoría son mayores que el ruido, entonces la inversión debe continuar usando modelos más complejos. También debemos esperar nuevos saltos cualitativos con la nueva generación de técnicas de inversión que incluyen la degradación espacial instrumental en el análisis. |
| Black holes in Horava gravity | Daniele Vernieri | Institut d'Astrophysique de Paris | 2016-09-29 | I will talk about black holes in Horava gravity which has been proposed as an ultraviolet completion to general relativity. Adding to the gravitational a ction higher -order spatial derivatives, without adding higher- order time derivatives, leads to a modification of the graviton propagator. The resulting theory is power -counting renormalizable at the expense of violating Lorentz symmetry at all scales, and, perhaps surprisingly, it appears to be phenomenologically viable in its more general form. It is really challenging to study the consequences of Lorentz invariance breaking in the case of black holes. In fact, in a Lorentz -violating gravity theory with higher- order dispersion relations, the event horizon relinquishes its role as an absolute causal boundary, since modes propagating infinitely fast will be able to penetrate it. However, this role will be taken over by the so called “universal horizon”. Because of the causal properties of such a spacetime, no signal can escape the interior of the universal horizon propagating to the exterior, no matter how fast it moves. So, the existence of the universal horizon is a strong indication that the notion of a black hole still makes sense in Horava gravity. |
| Space VLB interferometer RadioAstron: status and results | Yuri Y. Kovalev | Lebedev Physical Institute, Moscou, Rússia | 2016-06-07 | The RadioAstron Space VLBI mission utilizes the 10-m radio telescope on-board the dedicated Spektr-R spacecraft to observe cosmic radio sources with an unprecedented angular resolution at 92, 18, 6 and 1.3 cm. The longest baseline of the space-ground interferometer is about 350,000 km. I will briefly review basic parameters and capabilities of the space radio telescope Spektr-R and the RadioAstron interferometer. Science highlights of the mission will be presented. It includes exciting results on AGN, pulsars and interstellar scattering, cosmic masers. |
| Explosion and final state of the charged black hole bomb | Nicolás Sanchis Gual | Departament d'Astronomia i Astrofísica, Universitat de València | 2016-04-21 | I will present our results of a series of numerical relativity simulations of dynamical nonrotating black holes surrounded by self-gravitating scalar fields. In the non-charged case, even in the non-linear regime, quasistationary configurations of scalar fields are formed around black holes. Such configurations have been found to survive for cosmological time scales, which is a requirement for viable dark matter halo models in galaxies based on such types of structures. On the other hand, a Reissner-Nordström black hole (BH) is superradiantly unstable against spherical perturbations of a charged scalar field, enclosed in a cavity, with frequency lower than a critical value. We use the numerical relativity techniques to follow the development of this unstable system - dubbed charged BH bomb - into the non-linear regime, solving the full Einstein-Maxwell-Klein-Gordon equations, in spherical symmetry. |
| MHD instabilities in supernovae | Tomasz Rembiasz | Departament d'Astronomia i Astrofísica (UVEG) | 2016-03-11 | The magnetorotational instability (MRI) is one of the most promising agents amplifying the magnetic fields in a core-collapse supernova (CCSN) explosion. It was suggested that the MRI can be terminated by developing on top of the MRI structures parasitic instabilities of the Kelvin-Helmholtz (KH) or tearing mode (TM) type. We find that depending on the numerical setup, the MRI can be indeed terminated by KH instabilities or (driven by numerical resistivity) TMs. The latter, however, being unphysical under the CCSN conditions should be avoided in CCSN simulations. We study under which numerical conditions TMs driven by numerical resistivity can develop. We find that in MRI simulations with sufficiently low physical dissipation, MRI is terminated by KH instabilities (as theoretically expected for the CCSN conditions) and that the MRI can amplify the initial magnetic field only by a factor of the order of ten. |
| A survey of stellar tidal streams around nearby spiral galaxies | David Martínez Delgado | Zentrum für Astronomie der Universität Heidelberg, Alemanya | 2016-03-02 | |
| Reflections on the discovery of pulsars | Jocelyn Bell Burnell | Visiting Professor, Astrophysics, University of Oxford | 2016-02-10 | In this talk I will describe the discovery of pulsars (pulsating radio sources) and will also tell the stories of some 'near misses'. I will conclude by reflecting on what we can learn today from these stories. |
| 3D Supernova Simulations with CoCoNuT - Beyond the First Second | Bernhard Müller | Queen's University of Belfast | 2016-01-12 | The most popular scenario for core-collapse supernova explosions relies on the joint action of neutrino heating from the young neutron star and hydrodynamic instabilities like convection in the post-shock convection. We now see the advent of the first successful 3D simulations of these explosions using multi-group neutrino transport as required to accurately model neutrino heating and cooling. While it turned out harder to trigger shock revival in 3D than in axisymmetric 2D models, successful explosion models suggest that 3D effects can be helpful after shock revival for brining the simulations more in line with observed supernova explosion energies as I shall argue in this talk. Large-scale seed asymmetries from shell burning may help to raise explosion energies further by triggering shock revival earlier. I shall also outline feature of the parallel version of CoCoNuT employed for some of these simulations and discuss its performance on large HPC machines in Australia and Europe. |
| Magneto-elastic ray dynamics | Michael Gabler | Max Planck Institute für Astrophysik, Garching, Alemanya | 2015-12-11 | The study of wave equations in the short wave-length approximation is applied in many fields of physics. It is used in acoustics, microwaves, seismology and most extensively in quantum mechanics. The most obvious application, which should still be familiar to all of us, is the use of geometrical optics. The main idea is to write down the equations governing the dynamics in a Hamiltonian form, if necessary, by applying approximations. Solution techniques to solve integrable but also non-integrable (i.e. chaotic) Hamiltonian systems have been widely used and are very powerful. We would like to apply this technique to study the magneto-elastic oscillations of magnetars. We have set up a first magnetar-toy model, which already presents the characteristic properties of the set up we have studied in hydrodynamical simulations. |
| Galaxy clusters: thermodynamics of the hot gas | Veronica Biffi | Osservatorio Astronómico di Trieste, Itàlia | 2015-12-01 | Galaxy clusters can be a very powerful source of information for both cosmology and astrophysics, especially if results from both numerical simulations and observations are combined. To study clusters, the intra-cluster medium (ICM) filling their potential well is an optimal target, since it represents about 80 per cent of their visible baryonic matter and makes clusters very bright, extended X-ray sources in the Universe. Here, I will present results from numerical simulations and from synthetic X-ray data therefrom derived, which allows for faithful comparisons between simulated and observed clusters. With this kind of studies we can in fact address a number of interesting issues, such as the reconstruction of the ICM temperature distribution via spectral analysis, the investigation of scaling relations among global properties or the characterization of the gas non-thermal velocity field.Galaxy clusters: thermodynamics of the hot gas |
| Cold magnetized quark matter phase diagram within a generalized NJL model | Valeria Pagura | Departament de Física Teòrica, Universitat de València | 2015-09-30 | The influence of intense magnetic fields on the properties of strongly interacting matter has become an issue of increasing interest due to the fact that in some relevant physical situations like high energy non-central heavy ion collisions and compact stellar objects very strong magnetic fields may be produced. In this seminar I present some results of a study of the phase diagram of cold quark matter subject to intense magnetic fields in the framework of a generalized Nambu-Jona-Lasinio (NJL) model that includes flavor mixing effects and vector interactions. Charge neutrality and beta equilibrium effects, which are specially relevant to the study of compact stars, are also taken into account. |
| El origen de los chorros relativistas al desnudo | Iván Martí-Vidal | Onsala Space Observatory, Suècia | 2015-05-22 | Si bien los astrónomos llevamos más de 30 años estudiando los chorros relativistas en agujeros negros supermasivos, aún nos queda mucho que aprender sobre estos fascinantes astros. El modelo más aceptado de producción de chorros se basa en el llamado proceso de Blandford-Znajek que, aunque se entiende bastante bien a nivel energético, es algo elusivo en detalles a nivel de la dinámica del plasma. Según este modelo, intensos campos magnéticos en la parte más interna del disco de acrecimiento extraen energía rotacional del agujero negro y la transforman en la energía cinética de los chorros relativistas. Obviamente, el escrutinio de estos objetos a través de nuevas ventanas observacionales (con mayores sensibilidades y resoluciones) es esencial para el avance de la teoría y la correcta calibración de los modelos numéricos. Gracias a las técnicas de interferometría de muy larga base (VLBI) hemos podido reconstruir imágenes de las partes más internas de estos chorros relativistas (escalas de parsec), aunque gran parte de la información sobre el comportamiento de estos chorros en las inmediaciones del agujero negro (escalas del orden de la decena de radios de Schwarzschild) viene, bien de simulaciones y modelos, bien de extrapolaciones a partir de regiones muy distantes. La razón última de esto es que cerca del agujero negro, y a las típicas frecuencias de VLBI, el chorro absorbe completamente su propia radioemisión, por lo que resulta inobservable. En este seminario, plantearé los retos observacionales para el estudio de los chorros relativistas a las mayores frecuencias y discutiré las resoluciones alcanzables con la tecnología actual. Presentaré los nuevos resultados del estudio de variabilidad y polarización del blazar PKS1830-211 con ALMA, así como del potencial de las inminentes observaciones del centro galáctico (Sagitario A*) y del núcleo activo de M87 con VLBI milimétrico, usando ALMA en modo ""red en fase""(proyecto en el que participo en la parte de la calibración y análisis de los datos de polarización). El objetivo último es observar directamente, resolviendo espacialmente por primera vez, las regiones más próximas al horizonte de sucesos de un agujero negro. |
| Galaxies on FIRE (Feedback in Realistic Environments): The Role of Stellar Feedback in Dwarf Galaxy Formation | José Oñorbe | Max-Planck-Institut für Astronomie, Heidelberg (Alemanya) | 2015-05-07 | I will present hydrodynamical simulations of the formation of galaxies starting from cosmological initial conditions at high redshift. In these simulations, a novel numerical implementation of stellar feedback resulting from momentum imparted to the ISM by radiation, supernovae,and stellar winds has been used. Our ?nal objects have structure and stellar populations consistent with observed galaxies. Results indicate that feedback from massive stars plays a critical role in shaping the galaxy mass function, the structure of the interstellar medium (ISM), and the low e?ciency of star formation. I will focus the last part of my talk on the properties of the dwarf galaxies halos in the FIRE sample and its comparison with observations. |
| Multi-D Core-Collapse Supernova Models: where we are and where we are going? | Kei Kotake | Department of Applied Physics, Fukuoka University, Japan | 2015-03-25 | After we summarize a recent status of core-collapse supernova models, we report our recent results based on two-(2D) and three-dimensional (3D) radiation-hydrodynamics simulations. We also talk about signals of neutrinos and gravitational waves expected from the self-consistent models, which would be important to extract the information of the central engine from the multi-messenger observations. We also report our code development where 3D general-relativistic hydrodynamics is now meeting with spectral neutrino transport. |
| Coupling Non-thermal radiation to hydrodynamics | Valentí Bosch-Ramon | Departament d'Astronomia i Meteorologia, Universitat de Barcelona | 2015-03-23 | The calculations of the radiation from simplified semi-analytical, phenomenological, models of high-energy non-thermal sources, either galactic or extra-galactic, have allowed to put restrictions on or approximately characterize the main properties of the sources. However, more detailed treatments, necessary to full profit from multi-wavelength spectral and temporal data, require to account for the basic dynamical properties of the plasmas involved. In this talk, I will briefly introduce some examples of preliminary hydrodynamical calculations done accounting for the non-thermal component of the plasma, and show the high-energy non-thermal emission produced in those scenarios. |
| Termination of the magnetorotational instability via the parasitic Kelvin-Helmholtz instability in core-collapse supernovae | Tomasz Rembiasz | Max Planck Institut für Astrophysik, Garching, Alemanya | 2015-02-04 | Magnetorotational instability (MRI) is one of the most promising agents significantly amplifying magnetic fields in (resulting from rapidly rotating progenitors) core-collapse supernovae (CC-SNe). The initial phase of the MRI (of the exponential growth) is well understood, however its exact termination mechanism remains unknown. In this talk, we present our newest results clearly indicating that the MRI, given CC-SN conditions, is terminated by the parasitic Kelvin-Helmholtz instability. This allows us to set the limit on the maximum magnetic field amplification by the MRI. |
| Future stability of homogeneous cosmological models without a cosmological constant | Ernesto Nungesser | Trinity College Dublin, Irlanda | 2014-12-15 | There are several recent deep results concerning future stability of solutions to the Einstein-Vlasov and Einstein-Euler-system with a cosmological constant. In this talk we will present some results concerning the case of a vanishing cosmological constant and assuming that the spacetime is homogeneous. |
| The role of time-dependent injection in blazar flares | Michael Zacharias | Landessternwarte Konigstuhl, Heidelberg, Alemanya | 2014-09-18 | Rapid flaring events in blazars on timescales of a few minutes challenge the standard particle evolution scenarios of jets. Most new theories that can model the fast flares, depend on the underlying assumption of a continuous injection of particles. In this talk I will present analytical calculations on a time-dependent injection scenario. Since the electrons cannot reach equilibrium for non-continuous injection, the feedback with the radiative processes causes non-linear effects inducing a much quicker cooling of the electrons. The results are manifold: The total spectral energy distributions (SEDs) exhibit unique breaks, which would otherwise be modeled with a complicated electron distribution. Fractional SEDs, which are not integrated over the entire flare, indicate the need for the knowledge of the observation time relative to the onset of the flare. Otherwise, parameters and conclusions drawn from modeling might be wrong. The lightcurves show reduced variability timescales implying less extreme parameters as in other models. Lastly, I will briefly comment on the internal photon-photon absorption. It turns out that photon-photon absorption should not be a problem for the model. |
| Neutrino acceleration in collapsars | Yudai Suwa | Max Planck Institute for Astronomy, Garching (Alemanya) | 2014-09-11 | I will discuss about the possibility of neutrino acceleration from MeV to GeV due to (magneto-)hydrodynamic effects. This nonthermal component could significantly amplify the neutrino interaction (especially annihilation) rate. |
| Hartle's model within the general theory of perturbative matchings | Borja Reina | UPV/EHU | 2014-07-09 | Hartle's model [1] describes slowly rotating relativistic stars in the context of GR and essentially consists of the perturbative matching of a perfect fluid interior with an asymptotically flat vacuum exterior, up to second order in a rotation parameter. In the first part of this talk I will present the tools [2] needed to revisit this model from a consistent point of view and in the second one I will discuss the importance of the implicit assumptions made to construct the original model.[1] James B. Hartle The Astrophysical Journal 150 (1967) 1005-1029. [2] Marc Mars ""First and second-order perturbations of hypersurfaces""CQG 22 (2005) 3325'3347. |
| Pulsar Wind Termination Shocks | J.G. Kirk | Max Planck Institut fuer Kernphysik, Heidelberg, Alemanya | 2014-04-15 | Pulsar winds are made up of low density, magnetized, relativistic plasmas. When they impact the interstellar medium, they form a shock front which accelerates the particles responsible for Pulsar Wind Nebulae - the dominant galactic sources of very high energy gamma-rays. However, if the shock obeys the standard MHD jump conditions in a strongly magnetized plasma, it is not effective at dissipating the wind energy into particles. A way out of this problem is possible if the magnetic field arriving at the termination shock fluctuates on the rotation timescale of the pulsar, as expected in the 'striped wind' model. In this case, dissipation is possible either by driven reconnection in the compressed downstream plasma, or by conversion of the fluctuations into damped superluminal electromagnetic modes. In this talk, I will briefly describe the basic ideas behind pulsar wind theory, before discussing recent work on the role played by superluminal electromagnetic waves, and their possible radiative signatures. |
| Magnetorotational instability in Core-Collapse Supernovae | Tomasz Rembiasz | Max Planck Institute for Astrophysics, Garching bei Munchen, Alemanya | 2014-04-01 | The magnetorotational instability (MRI) is one of the most promising agents amplifying the magnetic fields in a core-collapse supernova explosion. Combining theoretical analysis and numerical simulations, we investigate whether magnetic fields can be increased to dynamically relevant strengths. We find that a secondary shear flow instability (Kelvin-Helmholtz) developing on top of MRI structures terminates the MRI driven amplification when the magnetic field strength has grown only by a constant factor of about twenty. |
| Radiative jet models for low-mass X-ray binaries | Gabriela Vila | Instituto Argentino de Radioastronomia | 2014-03-21 | X-ray binaries (XRBs) are systems formed by a compact object (a neutron star or a stellar-mass black hole) accreting from a non-collapsed companion. In some X-ray binaries, a fraction of the accretion flow is ejected from the surroundings of the compact object as two collimated jets that may reach velocities close to the speed of light. Such XRBs with jets are called microquasars. Microquasars emit electromagnetic radiation almost along the whole spectrum, from radio to X-rays. A few of them have also been detected at high and very high-energy gamma rays. It is usually accepted that the gamma rays are produced by relativistic particles accelerated in situ in the jets. In this talk, I will present the main features and results of a lepto-hadronic model for the electromagnetic radiation of jets in microquasars with low-mass companion stars. I will describe the channels of interaction of relativistic particles with matter, radiation, and magnetic field that are relevant under the physical conditions in the jets. The output of these processes is a complex broadband radiative spectrum. I will show the results of the model for some generic scenarios and specific applications to two well-studied X-ray transients. Motivated by the growing volume and quality of the data available at high and very high energies, I will focus on the predictions for the gamma-ray band and the chances of detecting these sources in the near future. Finally, I will briefly comment on the neutrino emission from microquasar jets. |
| Neutron star superfluidity: from cooling to glitches | Nils Andersson | University of Southampton | 2014-02-13 | In this talk, I will summarise our understanding of how observations can teach us about nucleon superfluidity at the extreme densities present in a neutron star's core. I will discuss the theory behind these systems, introducing the main ideas from nuclear physics and laboratory superfluids, and show how observations are beginning to constrain the theory in a useful way. The examples will involve the observed real-time cooling of the young neutron star in Cassiopeia A and the enigmatic glitches seen in many young radio pulsars. I will conclude by describing other settings where superfluidity is likely to play an important role. |
| PKS1830-211: Astrochemistry, fundamental physics, and jets, all at once | Ivan Marti Vidal | Onsala Space Observatory, Suècia | 2014-02-11 | The lensed blazar PKS1830-211 is a unique source in several aspects. It is very bright, even at sub-mm wavelenghts: the lens geometry is very well known, there is a strong molecular absorption from the lensing galaxy, and the lensed blazar is active in gamma rays. All these ingredients make this source extremely useful for the study of very different problems in Physics and Astronomy. I'll summarize the main results obtained by our group on the analysis of spectral-line and continuum mm/submm observations of PKS1830-211, using the SMA and ALMA, and will discuss on our future ALMA/VLBI projects. |
| Rayleigh-Taylor and Richtmyer-Meshkov Instabilities in Relativistic Hydrodynamic Jets | Jin Matsumoto | Astrophysical Big Bang Laboratory, RIKEN, Wako, Saitama, Japan | 2014-02-06 | We investigate the stability of relativistic jets using three-dimensional hydrodynamic simulations. The propagation of relativistic flow that is continuously injected from the boundary of computational domain into a uniform ambient medium is solved. An intriguing finding in our study is that Rayleigh-Taylor and Richtmyer-Meshkov type instabilities grow at the interface between the jet and ambient medium as a result of spontaneously induced radial oscillating motion. It is powered by in-situ energy conversion between the thermal and bulk kinetic energies. From complementary two-dimensional simulations of transverse structure of the jet, we find the effective inertia ratio of the jet to the surrounding medium determines a threshold for the onset of instabilities. The mixing between light faster jet and slow heavier external matters due to these instabilities causes the deceleration of the jet. |
| On the role of AGN feedback on the thermal and chemodynamical properties of the hot intracluster medium | Susana Planelles | Astronomy Unit, Department of Physics, University of Trieste, INAF-Osservatorio Astronomico di Trieste, Itàlia | 2013-12-19 | Reproducing the observed X-ray scaling relations, the cooling flow problem, and the different thermal properties of cool core and non-cool core clusters still represent a challenge for current cosmological simulations of galaxy clusters. In this talk, I will present the general analysis of a set of cosmological hydrodynamical simulations of galaxy clusters and groups, performed with the SPH GADGET-3 code, with the aim of studying the relative role played by different feedback sources on the general intracluster medium (ICM) properties: scaling relations, thermal radial profiles, and chemical enrichment. In order to do so, besides a set of non-radiative simulations, we carried out two sets of simulations including radiative cooling, star formation, metal enrichment and feedback from supernovae, one of which also accounts for the effect of feedback from active galactic nuclei (AGN) resulting from gas accretion onto super massive black holes. Our results confirm that including AGN feedback goes in the right direction of reconciling simulation predictions and observations for several observational ICM properties. However, a number of important discrepancies still exist, highlighting that the model needs to be improved to produce the correct interplay between cooling and feedback in central cluster regions. |
| Accretion in spacetimes with the cosmological constant | Patryk Mach | Jagiellonian University, Institute of Physics, Cracòvia, Polònia | 2013-11-21 | I will discuss spherical, isothermal and polytropic steady accretion models in the presence of the cosmological constant. Exact solutions are found for a class of isothermal fluids, assuming the test gas approximation. These results can have cosmological connotation, through the Einstein'Straus vacuole model of embedding local structures into FLRW spacetimes. In particular, one infers that steady accretion would not exist in the late phases of the Penrose’s scenario of the evolution of the Universe. If time permits, stability of the obtained solutions will be also discussed. |
| Star formation at radio wavelengths: proto-brown dwarfs and protoplanetary disks | Itziar de Gregorio-Monsalvo | ESO-ALMA | 2013-11-07 | I will present my latest studies on two different topics: the formation of brown dwarfs (BDs) and the structure of the protoplanetary disks. The formation of BDs is currently a hot topic of research. Since stars and BDs evolve very rapidly during the first million years, many answers to the formation mechanism must come from the study of their properties when they are deeply embedded in the natal cloud (proto-BD stage). Sensitive millimeter and submillimeter surveys offer the exciting prospect of identifying a population of candidate proto-BDs for the first time, as well as studying BD disk properties. In this talk I will present a multiwavelength study in Taurus, Chamaeleonis II and Barnard 30 star forming regions aiming to search for the best proto-BD candidates of the region. As a second topic, I will show the results of very high-resolution and sensitive observation using ALMA towards the disk surrounding the intermediate mass young star HD163296. Dust and gas-rich disks around recently-formed stars are important as they harbor planets either recently formed or in the process of formation. Consequently, the structure of these young protoplanetary disks has been the subject of intense study over a wide range of wavelengths. HD163296 is one of the best-studied protoplanetary disks, and was one of the first to be resolved with mm-interferometry. I will present the detailed radial and vertical structure of this protoplanetary disk and the implications of these results for current theoretical models. |
| News of ALMA from an insider | Itziar de Gregorio-Monsalvo | ESO-ALMA | 2013-11-05 | The Atacama Large Millimeter/submillimeter Array (ALMA) is an international partnership of Europe, North America ,and East Asia in cooperation with the Republic of Chile. ALMA is a telescope of revolutionary design. It will be composed initially of 66 high precision antennas located on the Chajnantor plateau, 5000 meters altitude in northern Chile. ALMA will observe at wavelengths in the range 3 mm to 400 ?m (84 to 720 GHz) and will be 10-100 times more sensitive and will have 10-100 times better angular resolution than current millimeter interferometers. The design of ALMA is driven by three key science goals: The ability to detect spectral line emission from CO or [CII] in a normal galaxy like the Milky Way at a redshift of z=3 in less than 24 hours, the ability to image the gas kinematics in protostars and in protoplanetary disks around young Sun-like stars in the nearest molecular clouds (150 pc), and the ability to provide precise high dynamic range images at an angular resolution of 0.1 arcsec. ALMA Early Science operations started on September 2011 and yielded more than 60 publications in refereed journals so far. In this talk, I will present the ALMA history, its current status, and I will give a general overview on the capabilities offered in the next Cycle 2 call for proposal. |
| Simulación del efecto del acrecimiento de masa en estrellas de tipo solar | Ana Inés Gómez de Castro | Departamento de Física de la Tierra, Astronomía y Astrofísica I, Sección Departamental de Astronomía y Geodesia, Universidad Complutense de Madrid | 2013-10-28 | En este seminario presentaré la evolución de modelado analítico a la simulación numérica del proceso de acrecimiento en las estrellas pre-secuencia principal de tipos tardíos. Dentro de este marco, me centraré en el trabajo realizado por nuestro grupo en el estudio de los vientos y la eyección de materia. |
| Optical photometric monitoring of LS I +61 303 | Xavier Paredes Fortuny | Departament d'Astronomia i Meteorologia, Universitat de Barcelona | 2013-10-25 | Four gamma-ray binaries, namely PSR B1259-63, HESS J0632+057, HD 215227 and LSI+61 303, contain compact objects orbiting around massive Be stars. The nature of the compact object is only known in the case of PSR B1259-63, but the other systems could also contain young non-accreting pulsars with relativistic winds. Around periastron passage the compact objects should produce significant changes in the structure of the Be disks due to gravitational forces and eventually by ram pressure from the pulsar wind. Accurate photometry could be used to constrain the shape of the disk during the periastron passage. In this talk I present an ongoing program to monitor the optical photometry of gamma-ray binaries and show preliminary results for the case of LS I+61 303. I will also briefly talk about my work here, related with relativistic hydrodynamic simulations of these systems. |
| Superfluid Magnetars and QPO spectrum | Andrea Passamonti | INAF-Osservatorio Astronomico di Roma, Itàlia | 2013-10-10 | The analysis of Quasi Periodic Oscillations (QPOs) in Magnetars provided the first application of Asteroseismology in neutron stars. These oscillations are likely identified with magneto-elastic waves which originate from the giant flares. Recent cooling calculations show that heat generated by magnetic field decay does not prevent the superfluid transition of the magnetar's core. This means that realistic models of magnetars should include superfluid/superconducting constituents in order to extract information from QPO observations. In this talk, I report our results on the oscillation spectrum of superfluid and magnetised neutron stars and the implications of superfluid physics on the QPOs. |
| Numerical relativity in spherical polar coordinates: calculations with the BSSN formulation | Pedro Montero | Max Planck Institut für Astrophysics, Garching, Alemanya | 2013-09-19 | I report on an implementation of the BSSN equations coupled to the general relativistic hydrodynamic equations in spherical polar coordinates without any symmetry assumptions. Using a PIRK method and a reference-metric approach we obtain stable simulations in three spatial dimensions without the need to regularize the origin or the axis. We perform and discuss a number of tests to assess the stability, accuracy and convergence of the code. |
| Multi Scale Fluid Kinetic Simulation Suite. An introduction to the Programmer's Guide. | Dr. Sergey Borovikov | CSPAR - University of Alabama in Huntsville, USA | 2013-07-24 | We will focus on internal structure of the MS-FLUKSS. Starting from the main function, will investigate how everything is initialized, what are mechanisms to create your problem, Riemann solver, reconstruction subroutines, source terms and all other aspects of the adding new functionality of the code. |
| SHARDS: a GTC Ultra-deep Spectro-photometric Survey of Distant Galaxies | Antonio Cava | Departamento de Astrofísica, Universidad Complutense de Madrid | 2013-05-22 | In this talk I will introduce the SHARDS (Survey for High-z Absorption Red & Dead Sources, Perez-Gonzalez P.G., Cava A., Barro G. et al. 2013) project, an unbiased ultra-deep spectro-photometric survey with OSIRIS@GTC aimed at selecting and studying massive passively evolving galaxies at z=1.0-2.3 using a set of 24 medium-band filters (FWHM ~17 nm) at 500-950 nm in GOODS-N. Our observing strategy is optimized to detect at z>1 the prominent MgUV absorption feature at rest-frame ~280 nm, a distinctive, necessary, and sufficient feature of evolved stellar populations. Nonetheless, the data quality allow a plethora of studies on galaxy populations, including Emission Lines Galaxies (ELGs) about which we have started one of our first science verification projects. The first analysis of ELGs in SHARDS, demonstrate the huge capability of this survey in providing physical information for a large sample of emitters, spanning from local H_alpha to high-z Lyman-alpha emitters. |
| Zooming in on in AGN structure with microlensing | Ana Mosquera | Department of Astronomy, The Ohio State University | 2013-05-13 | The main observational problem for testing accretion disk models lies in the inability to resolve the emission regions of quasars, since no astronomical method allows us to direct imaging their central engine. In this talk I will review how gravitational microlensing provides a natural telescope to zoom in on in the regions closest to the SMBH and its implications. |
| Jets from X-ray Binaries | Simone Migliari | Departament d'Astronomia i Meteorologia, Institut de Ciències del Cosmos, Facultat de Física, Universitat de Barcelona | 2013-03-08 | Jets are possibly the most spectacular and powerful phenomena in astrophysics. They are ubiquitous in the universe, common to a number of different accreting objects, from non-relativistic to relativistic systems, such as young stellar objects, cataclysmic variables, X-ray binaries and active galactic nuclei. However, the mechanism(s) of jet production is still poorly understood. In the search for the elements and parameters contributing to the formation of jets, key is the cross comparison of the different jet systems. The accretion disk is a common denominator for all these sources and seems to be essential to the formation of their jets. However, differences in the jet behaviour among these systems, indicate that also parameters proper of the accreting star might play a role in the jet production. I will give an overview of our observational knowledge of jets through studies of X-ray binaries. |
| The Principle of General Covariance and the Hole Argument | Alberto Chamorro | Department of Theoretical Physics, University of the Basque Country | 2013-03-06 | This is part of a paper of the speaker recently published on the meaning of the Principle of General Covariance (GCP) where a precise formulation of that principle as a General Relativity Principle is put forward. We start by explaining that formulation with the help of a natural extension of the Minkowskian coordinates used in flat space-time to general curved space-times that we call quasi-Minkowskian coordinates. Then we review the history and debate around the Hole Argument (HA) describing its rationale and the difficulties to accept a general covariant theory to which it supposedly leads. By resorting to the quasi-Minkowskian coordinates above mentioned we show how the whole issue posed by the HA is greatly clarified and how it is the metric that supplies the physical meaning of coordinates and individuates point-events in regions of space-time where no other fields exist. The talk ends arguing in favour of interpreting the GCP not only as a predictive physical principle, but also as a guiding principle supporting Einstein's appreciation of its heuristic worth in his reply to Kretschmann in 1918. |
| Magneto-Rotational-Instability in Magnetized Hypermassive Neutron Stars | Riccardo Ciolfi | Albert Einstein Institute, Potsdam, Alemanya | 2013-02-05 | Differentially rotating hypermassive neutron stars (HMNSs) are metastable configurations which can be formed in the latest stage of binary neutron star mergers. Their eventual collapse produces a spinning black hole surrounded by a hot and thick accretion disk. The dynamics of such a system is of crucial importance, since it could generate the relativistic jets observed in short gamma-ray bursts. By performing simulations of very high resolution, we study the influence of magnetic fields on the evolution of HMNSs. In particular, we provide convincing evidence for the occurrence of the magneto-rotational instability (MRI), potentially responsible for strong magnetic field amplification and angular momentum redistribution. Characteristic features of the MRI are discussed and quantities such as the characteristic growth rate and the wavelength of the fastest growing mode are extracted and compared with analytical predictions. |
| Implicaciones astrofísicas en el estudio de las condritas carbonáceas: el interés en la misión Marco Polo-R de la ESA | Josep M. Trigo Rodríguez | Institut d'Estudis Espacials de Catalunya (CSIC-IEEC) | 2012-12-04 | Ciertos grupos de condritas carbonáceas proceden de pequeños asteroides y quizás de cometas que en algún momento estuvieron empapados en agua hasta el punto que se produjo la alteración acuosa de sus minerales constituyentes. Por ejemplo, dentro del grupo CR de esas condritas el meteorito GRA 95229 parece poseer una complejidad orgánica no vista antes en ningún otro meteorito, ni siquiera en el famoso Murchison caído en 1969. Presentaré los estudios que estamos realizando sobre ambos meteoritos en laboratorios del CSIC donde encontramos materiales presolares junto a compuestos orgánicos presumiblemente catalizados durante la alteración acuosa de su asteroide progenitor. Recuperar tales materiales sin sesgos es precisamente el objetivo de la misión Marco Polo-R de retorno de muestras de un asteroide primitivo que decide su futuro y objetivos en un próximo simposio en Barcelona |
| Centaurus A's Jet on Subparsec Scales | Cornelia Müller | Dr. Remeis Observatory Bamberg, University of Erlangen-Nürnberg, Germany | 2012-11-26 | I will talk about black holes in Horava gravity which has been proposed as an ultraviolet completion to general relativity. Adding to the gravitational a ction higher -order spatial derivatives, without adding higher- order time derivatives, leads to a modification of the graviton propagator. The resulting theory is power -counting renormalizable at the expense of violating Lorentz symmetry at all scales, and, perhaps surprisingly, it appears to be phenomenologically viable in its more general form. It is really challenging to study the consequences of Lorentz invariance breaking in the case of black holes. In fact, in a Lorentz -violating gravity theory with higher- order dispersion relations, the event horizon relinquishes its role as an absolute causal boundary, since modes propagating infinitely fast will be able to penetrate it. However, this role will be taken over by the so called “universal horizon”. Because of the causal properties of such a spacetime, no signal can escape the interior of the universal horizon propagating to the exterior, no matter how fast it moves. So, the existence of the universal horizon is a strong indication that the notion of a black hole still makes sense in Horava gravity." |
| Masers in Evolved Stars | Jean-François Desmurs | Observatorio Astronómico Nacional, Madrid | 2012-11-07 | Asymptotic Giant Branch (AGB) stars are the final evolution stage of low and intermediate mass stars. During this phase, they lose a lot of matter in the form of stellar winds. As the atmosphere of these stars is enriched by convection from the elements synthesized in their core, this mass loss enriches the interstellar medium of the Galaxy in heavy elements, oxygen, carbon, dust... Astrophysical masers are characterized by showing very large brightness equivalent temperatures. This property of the maser emission has been extensively used to probe the inner shells of the thick circumstellar envelopes that surrounds AGB and post-AGB sources. They provide excellent tracers of the dynamic of the envelope at different distances from the central stars. These regions are of particular interest, since it is where the processes of dust formation and gas acceleration (responsible for the mass loss of the star and the formation of the envelope) occur. I will discuss the different circumstellar masersobserved and how we can use them as astronomical tools to probe in-situ different physical parameters. |
| RadioAstron Space VLBI mission: current status, early science results, AO-1 | Y. Y. Kovalev | Astro Space Center, Lebedev Physical Institute, Moscou, Rússia | 2012-11-05 | The 10-meter space radio telescope Spektr-R was successfully launched on July 18, 2011, and unfurled several days later. The space element of the ground-space VLB interferometer RadioAstron covers four frequency bands from 0.3 to 25 GHz and provides baselines up to 350,000 km. This will allow to study space objects with a resolution as high as about 10 microarcsecond. In-orbit tests of the space craft are finished, first fringes are found at all four bands of 92, 18, 6, and 1.3 cm. Current status of the mission and plans to move to the open sky phase by 2013 will be discussed. Science objectives and first results of the RadioAstron early science program will be presented. |
| Dinnertime for SgrA* (The Black Hole in the Center of OUR Galaxy) | James Moran | Harvard-Smithsonian Center for Astrophysics | 2012-10-02 | I will describe the developing efforts to image the environs of the black hole in the center of our galaxy at 230 GHz and higher with Very Long Baseline Interferometry (VLBI). The VLBI Array is called the Event Horizon Telescope (EHT). At 230 GHz the interstellar scattering and the source optical depth are sufficiently small that the immediate vicinity of the black hole can be discerned. The size of this image has a diameter of about 37 microarcseconds or about 4 Schwarzschild radii. Image quality should improve rapidly in the coming years as the EHT is formed and may provide new insight about general relativity in the strong gravity limit. We are at a phase of development similar to that of imaging Cygnus A in the early 1950s. Plans are under way to image SgrA* next spring when the newly discovered orbiting earth-sized mass, now known as ""G2"", will be tidally disrupted as it passes perihelion and may cause electromagnetic flaring activity. I will also describe the imaging of the innermost parts of the jets driven by the black holes in M87 and another AGN, 1924-293. |
| Jet Precesion in the AGN of M81. Physical Parameters and Evidence of a Binary Black Hole | Ivan Marti-Vidal | Onsala Space Observatory (Chalmers University), Onsala, Suècia | 2012-07-18 | We report on a full campaign of multi-frequency global-VLBI observations of M81, phase-referenced to the closeby supernova SN1993J. From these observations, we find a systematic drift in the intensity peak of M81 among the different frequencies (possibly due to opacity effects in the radio jet). From these results, we can estimate the mass of the central black hole and the strength of the magnetic field at the jet base. The former is compatible with previous estimates using independent approaches (the latter is about 4 orders of magnitude higher than previous estimates). Furthermore, from the astrometry to SN1993J, we also detect an evolution in the jet position angle that is correlated to changes in the total flux density of M81 and to changes in the orientation of the jet cores at all frequencies. These results can be interpreted as due to jet precesion, with a period of a few decades. Indeed, from the modelling of the core orientation vs. time, we also detect strong evidence of two different period contributions to the jet precesion (binary black hole in M81?!). Further results on the astrometry monitoring of M81, now phase-referenced to a new closeby supernova, are also being analyzed. We are also analyzing radio light curves of M81 (with the VLA, covering almost 12 years at frequencies ranging from 300MHz to 22GHz), to help us better constrain the physical parameters and evolution of the jet in M81. |
| Análisis de la cinemática y la emisión del jet del blázar B1551+130 | Shaun Nicol | Imperial College London | 2012-07-02 | (Presentación oral del proyecto de investigación como estudiante de intercambio 'One year in Europe') En este trabajo se presentan los resultados del estudio del jet relativista del blázar B1551+130 (z=1.308) a partir de seis observaciones del VLBA a 15 GHz en el marco del proyecto MOJAVE, entre junio de 2009 y abril de 2010. Se presentan resultados sobre movimientos superlumínicos en el jet de hasta 10c, así como una determinación del ángulo de visión del jet, estimado en 5.6º, y el consiguiente factor de reforzamiento Doppler en la emisión. Se discuten movimientos aparentes negativos en el jet en la región más cercana a su núcleo de radio. Se concluye comparando los resultados obtenidos mediante radiointerferometría con observaciones paralelas en rayos gamma del satélite Fermi y también con la distribución espectral de energías a lo largo de todo el espectro electromagnético. |
| Relativistic collapse and explosion of rotating supermassive stars with thermonuclear effects | Pedro Montero | Max-Planck-Institut für Astrophysik, Garching, Alemanya | 2012-06-28 | We present results of general relativistic simulations of collapsing supermassive stars with and without rotation using the two-dimensional general relativistic numerical code Nada, which solves the Einstein equations written in the BSSN formalism and the general relativistic hydrodynamics equations with high resolution shock capturing schemes. These numerical simulations use an equation of state which includes effects of gas pressure, and in a tabulated form those associated with radiation and the electron-positron pairs. We also take into account the effect of thermonuclear energy released by hydrogen and helium burning. We find that objects with a mass of 5x10^{5} solar mass and an initial metallicity greater than Z_{CNO}~0.007 do explode if non-rotating, while the threshold metallicity for an explosion is reduced to Z_{CNO}~0.001 for objects uniformly rotating. The critical initial metallicity for a thermonuclear explosion increases for stars with mass ~10^{6} solar mass. For those stars that do not explode we follow the evolution beyond the phase of black hole formation. We compute the neutrino energy loss rates due to several processes that may be relevant during the gravitational collapse of these objects. The peak luminosities of neutrinos and antineutrinos of all flavors for models collapsing to a BH are ~10^{55} erg/s. The total radiated energy in neutrinos varies between ~10^{56} ergs for models collapsing to a BH, and ~10^{45}-10^{46} ergs for models exploding. |
| The Kepler Mission: Overview and Results | Guillermo Torres | Harvard-Smithsonian Center for Astrophysics | 2012-06-22 | The search for planets around other stars has taken a giant leap forward with the launch of NASA's Kepler Mission, which has been in operation for 3 years. I will review some of its most exciting discoveries in the field of transiting planets, including multiple systems, planets in the habitable zone of their parent stars, rocky planets that are smaller than the Earth, and tantalizing evidence that small planets like the Earth may be common around Sun-like stars. |
| Stability of Iterative Algorithms for Rotating and Binary Neutron Stars | Charalampos Markakis | SFB/TR7 Gravitational Wave Astronomy, Theoretical Physics Institute, University of Jena, Alemanya | 2012-05-31 | Similar methods have been used to construct models of rapidly rotating or binary stars, in Newtonian and relativistic contexts. The choice of method has been based on numerical experiments, which indicate that particular methods converge quickly to a solution, while others diverge. The theory underlying these differences, however, has not been understood. In an attempt to provide a better theoretical understanding, we analytically examine the behavior of different iterative schemes near an exact static solution. We find the spectrum of the linearized iteration operator and show for self-consistent field methods that iterative instability corresponds to unstable modes of this operator. Minimizing the maximum eigenvalue accelerates convergence and allows computation of highly compact configurations that were previously inaccessible via self-consistent field methods. |
| Unification scenarios of Active Galactic Nuclei: an X-ray view | Claudio Ricci | ISDC - Science data center for Astrophysics, University of Geneva, Switzerland | 2012-05-23 | Active Galactic Nuclei (AGN) are the most luminous persistent sources of radiation in the Universe. The unified model of AGN foresees that different types of AGN are intrinsically the same object, and that observational differences are solely due to different inclination angles with respect to an obscuring toroidal structure. However, recent results have shown that the anisotropic absorber appear to be clumpy and to have covering factors inversely proportional to the luminosity. The hard X-rays (>10 keV) are a very suitable energy band for studying the unified model. Absorption does not play an important role at these energies, allowing to have a direct look at the central engine of the AGN. By analyzing the INTEGRAL IBIS/ISGRI average hard X-ray (17-250 keV) spectra of ~200 radio-quiet local AGN, we recently found that more obscured AGN have a larger reflection component than less obscured ones, which cannot be easily explained by the unified model, but might require an intrinsic difference in the covering factor of the torus between different types of AGN. In my talk, I will present several unification scenarios, and discuss their possible relation with the observed decrease of the equivalent width of the iron Kalpha line with the luminosity (i.e. the X-ray Baldwin effect). |
| An ultra-deep view of disk galaxies: what is out there? | Ignacio Trujillo | Instituto de Astrofísica de Canarias | 2012-05-11 | In the last years, there is a growing consensus that our traditional picture of disk galaxies being purely described by an exponential decline in brightness is unsustainable. In fact, the nature of the outer regions of the spiral galaxies seem to be much richer both in shapes and in stellar population properties. All this richness informs us about the way disk galaxies are assembled over time. I will summarize what we have learned recently about the nature of the outer regions of the spiral galaxies, putting a particular focus into a set of new deep observations with the SDSS Stripe82 reaching 30 mag/arcsec^2. |
| Stellar tidal streams in nearby galaxies: mapping the minor merger rate in the local Universe with small telescopes | Dr David Martinez-Delgado | Max-Planck Institut für Astronomie, Heidelberg, Alemanya | 2012-04-27 | Within the hierarchical framework for galaxy formation, minor merging and tidal interactions are expected to shape large galaxies to this day. As part of a pilot survey, we have carried out ultra-deep, wide-field imaging of some isolated spiral galaxies similar to the Milky Way in the local universe with data taken at small (0.1 to 0.5-meter diameter), robotic telescopes that provide exquisite surface brightness sensitivity. Our observational effort has led to the discovery of previously undetected giant stellar structures in the halos of these galaxies, likely associated with debris from tidally disrupted satellites. Our collection of galaxies presents an assortment of tidal phenomena exhibiting strikingly diverse morphological characteristics. The comparison with available stellar halo simulations set in a Lambda-Cold Dark Matter cosmology suggests that this extraordinary variety of morphological specimens detected in our survey could represent one of the first comprehensive pieces of evidence to support that the hierarchical formation scenarios predicted for the formation of galaxies similar to our Galaxy. I also present the discovery of a tidal stream around a nearby dwarf irregular galaxy with our small telescopes. Follow-up observations with Subaru telescope show this stream completely resolved into stars, providing observational evidence of a minuscule merger in a LMC-type system in the local universe. This result suggests that dwarf accretion could play an important role in the star formation history and evolution of nearby dwarf galaxies. |
| Spectral Evolution in Blazars | Christian M. Fromm | MPI für Radioastronomie, Bonn, Alemanya | 2012-04-03 | The spectral evolution in Blazars is usually studied by large multi-frequency campaigns across the electro-magnetic spectrum. However, these observations cannot resolve the structure of the jets. For our study we used a different approach based on multi-frequency VLBI observations covering a frequency range form 2 GHz to 86 GHz, which allow to analyze both, the temporal and spatial spectral evolution. We developed several analysis tools to extract the spectral parameters and applied it to the 2006 radio flare in CTA 102. In the talk we will present the first results of this study. |
| Nonlinear damping of neutron star oscillations | Wolfgang Kastaun | Albert Einstein Institut (Alemanya) | 2012-02-24 | Oscillations of neutron stars are a possible source of detectable gravitational waves due to the existence of a gravitational-rotational instability which transfers energy from the rotation of a star into gravitational waves and oscillation energy. There are however several effects that could suppress the growth of those instabilities already at low amplitudes, e.g. viscosity, mode coupling, or superfluidity effects. Those mechanisms depend on physical parameters not exactly known and/or are difficult to estimate even for given parameters due to the long timescales involved. We instead investigated generic hydrodynamic effects active at very high amplitudes, such as shock formation or breaking of surface waves, in order to provide absolute upper limits on the gravitational wave luminosity of oscillating neutron stars. |
| How relevant are barotropic models for magnetised neutron stars? | Sam Lander | Universität Tübingen (Alemanya) | 2012-02-23 | Many aspects of NS physics are sensitive to the internal structure of their magnetic fields, although we have no direct probe of these. Instead we rely on theoretical models, where the star is usually assumed to have a barotropic equation of state: pressure is a function of density alone. Many magnetic equilibria have been constructed in this way, and whilst some are known to be *unstable*, none have been proved stable - and hence good physical models. We discuss testing the stability of these candidate equilibria, in the search for an astrophysically relevant model of a NS's magnetic field. |
| Self-gravitating Tori around black holes and their instabilities | Nikolaos Stergioulas | Aristotle University of Thessaloniki, Grècia | 2012-02-22 | We give an overview of recent progress in constructing equilibrium models of self-gravitating tori around black holes, using a self-consistent field method. We focus on the properties of models with constant specific angular momentum that exactly fill their Roche lobe and show that their angular momentum is limited in the same way as in the case of a fixed background metric. Furthermore, we explore the stability of such disks against runaway and nonaxisymmetric instabilities using three-dimensional hydrodynamics simulations in full general relativity. All of our models develop unstable nonaxisymmetric modes on a dynamical time scale.We observe two distinct types of instabilities: the Papaloizou-Pringle and the so-called intermediate type instabilities. The development of the nonaxisymmetric mode with azimuthal number m=1 is accompanied by an outspiraling motion of the black hole, which significantly amplifies the growth rate of the m=1 mode in some cases. We comment on the generation of gravitational waves and on the development of the runaway instability |
| Partially implicit high order Runge-Kutta methods for wave-like equations in spherical-type coordinates | Isabel Cordero-Carrión | Max Planck Institute for Astrophysics, Garching (Alemanya) | 2012-01-13 | I will present new partially implicit Runge-Kutta high order methods in order to numerically evolve in time a set of partial differential equations. These methods are based on the ideas used in Cordero-Carrión et al. (2011) to evolve numerically the hyperbolic sector of the metric in the so called Fully Constrained Formulation of Einstein equations, and are designed in order to overcome numerical instabilities, due, for example, to potential numerical unstable terms in the sources of the system or to effects of the chosen system of coordinates (as it was our case). |
| GRB 101225A: a stellar murder on Christmas Day | Miguel Ángel Aloy | Departament d'Astronomia i Astrofísica, Universitat de València | 2011-12-15 | Long Gamma-Ray Bursts (GRBs) are the most dramatic examples of massive stellar deaths, usually associated with supernovae (Woosley et al. 2006). They release ultra-relativistic jets producing non-thermal emission through synchrotron radiation as they interact with the surrounding medium (Zhang et al. 2004). Here we report observations of the peculiar GRB 101225A (the 'Christmas burst'). Its gamma-ray emission was exceptionally long and followed by a bright X-ray transient with a hot thermal component and an unusual optical counterpart. During the first 10 days, the optical emission evolved as an expanding, cooling blackbody after which an additional component, consistent with a faint supernova, emerged. We determine its distance to 1.6 Gpc by fitting the spectral-energy distribution and light curve of the optical emission with a GRB-supernova template. Deep optical observations may have revealed a faint, unresolved host galaxy. Our proposed progenitor is a helium star-neutron star merger that underwent a common envelope phase expelling its hydrogen envelope. The resulting explosion created a GRB-like jet which gets thermalized by interacting with the dense, previously ejected material and thus creating the observed black-body, until finally the emission from the supernova dominated. An alternative explanation is a minor body falling onto a neutron star in the Galaxy (Campana et al. 2011). |
| Infrared spectro-interferometry of AGB stars | Markus Wittkowski | European Southern Observatory, Garching bei München, Alemanya | 2011-11-23 | Mass loss from asymptotic giant branch (AGB) stars is the most important driver for the evolution of evolved low to intermediate mass stars toward planetary nebulae. It is also one of the most important sources of the chemical enrichment of the interstellar medium. The mass-loss process originates in the extended atmospheres, whose structure is affected by stellar pulsations, and where molecular and dusty layers are formed. Optical interferometry resolves the extended atmospheres of AGB stars and thereby enables us to obtain measurements of the intensity profile across this region. I will present recent near- and mid-infrared spectro-interferometric observations of AGB stars. These observations indicate a stellar intensity profile consistent with predictions of the latest dynamic model atmospheres based on self-excited pulsation models, and allow us to characterize the inner circumstellar dust shell. The AMBER data also show non-zero closure phases, which are indicative of deviations from point symmetry at all wavelengths, thus a complex non-spherical stratification of the extended atmosphere. We interpret these inhomogeneities as the result of pulsation- and shock-induced chaotic motion in the extended atmosphere. During this talk I will also describe the current status of the ESO VLT Interferometer and future plans. |
| High-energy emission from relativistic outflows in compact environments | Valentí Bosch-Ramon | Dublin Institute for Advanced Studies, Irlanda | 2011-10-27 | Relativistic outflows produced in binary systems, or the SMBH in the center of AGN, are subject to violent disturbances due to the crowded media in which they are embedded. The direct impact or the entrainment of external matter by these outflows lead to strong hydrodynamical perturbations and energy dissipation. This energy can be partially channelled into non-thermal particles that will produce emission from radio to very high energies via different processes. In this talk, I will briefly discuss some interaction scenarios in the context of relativistic outflows in compact environments, focusing on the evolution of the flows involved, and on the high-energy non-thermal processes. |
| El Centro de Estudios de Física del Cosmos de Aragón y el Observatorio Astrofísico de Javalambre | Mariano Moles | CEFCA, Centro de Estudios de Física del Cosmos de Aragón | 2011-10-20 | |
| Photospheric Thermal Radiation From GRB Collapsar Jets | Akira Mizuta | Theory Center, Institute of Particle and Nuclear Studies, KEK (High Energy Accelerator Research Organization), Japan | 2011-07-25 | The gamma-ray bursts (GRBs) are one of the most luminous events in the universe. The radiation mechanism of GRB prompt emission is still underdebate. If a central engine makes a fireball, we can expect strong thermal emission from the photosphere. We have performed numerical hydrodynamic simulations of GRB jet propagation from collapsars and have derived photospheric thermal radiation by the post process. The light curves and spectra are derived for the observers at different viewing angles. We observe a few seconds time variability in the light curves caused by the internal mass density and Lorentz factor discontinuities in the jets.When we plot E_p-E_{iso} or E_p-L_{iso}_p, we can see similar dependence with empirical GRB cosmological relations such as Amati relation and Yonetoku relation. |
| Dark Matter and Hidden Photons with Radio Observations | A.P. Lobanov | Max-Planck-Institut für Radioastronomie, Bonn, Alemanya | 2011-07-21 | Providing observational evidence for physics beyond the standard model is one of the pivotal research areas in modern particle physics and cosmology. Weakly interacting (massive or sub-eV) particles (WIMP or WISP), such as neutralinos. Most extensions of the standard model beyond the electroweak scale (most notably the supersymmetric and string theory models) predict existence of weakly interacting particles responsible for coupling to the SM physics, with WIMP (e.g., neutralinos with masses in the GeV to TeV range) and WISP (e.g., axions, axion-like particles and hidden photons with masses in the sub-eV range) positioned as the most promising candidates. A new dimension to searches for WIMP and WISP is provided by extending the searches to lower energies sampled by radio observations atfrequencies below 40 GHz (7.5 mm). Observations in the 0.03-40 GHz bear an excellent potential to constrain the properties of the neutralino dark matter (DM) annihilation and offer an effective way of probing the hidden photons with masses below 10-15 eV. Potentials and early results from such studies will be discussed in this talk, focussing in particular on detecting the neutralino DM annihilation signal from dwarf spheroidal galaxies and unidentified Fermi/LAT gamma-ray sources and searching for WISP photon-photon oscillations in the radio regime using supernova remnants and active galactic nuclei. |
| Radio transients from stellar tidal disruption by supermassive black holes | Dimitrios Giannios | Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, USA | 2011-07-13 | The tidal disruption of a star by a supermassive black hole provides us with a rare glimpse of these otherwise dormant beasts. It has long been predicted that the disruption will be accompanied by a thermal 'flare', powered by the accretion of bound stellar debris. Several candidate disruptions have been discovered in this manner at optical, UV and X-ray wavelengths. Here we explore the observational consequences if a modest fraction of the accretion power is channeled into an ultra relativistic outflow. We show that a relativistic jet decelerates due to its interaction with the interstellar medium at sub-parsec distances from the black hole. Synchrotron radiation from electrons accelerated by the reverse shock powers a bright radio-infrared transient that peaks on a timescale ~1 yr after disruption. Emission from the forward shock may be detectable for several years after the peak. Deep radio follow-up observations of tidal disruption candidates at late times can test for the presence of relativistic ejecta. Upcoming radio transient surveys may independently discover tens to hundreds of tidal disruptions per year, complimenting searches at other wavelengths. Non-thermal emission from tidal disruption probes the physics of jet formation under relatively clean conditions, in which the flow parameters are independently constrained. |
| Estudio de VLBI del jet relativista en el núcleo activo de galaxia 4C +21.78 | Indy Leclercq | Imperial College London & Universitat de València | 2011-06-22 | Observaciones del blázar 4C+21.78 (B1222+216) realizadas por el observatorio espacial Fermi en rayos gamma muestran una erupción en esta banda durante los últimos meses (Astronomer's Telegram 2021, 2349, 2584 y 2687). El seguimiento en radiofrecuencia realizado por el Radio Observatorio de la Universidad de Michigan muestra también un fuerte crecimiento en el brillo a longitudes de onda centimétricas. Se presentan resultados del cartografiado híbrido y del modelado de la distribución de brillo del jet relativista de esta radiofuente a partir de datos tomados por el proyecto MOJAVE durante los últimos tres años. Se analizará en detalle la cinemática de las distintas regiones del jet a partir de los modelos realizados, y se compararán los resultados con las observaciones previas a la erupción de rayos gamma y publicadas por el equipo de MOJAVE (Lister et al. 2009). (Proyecto de investigación de estancia Erasmus, 3r año de grado) |
| Relativistic plasma dynamics in Pulsar Wind Nebulae and in long GRB projenitors | Prof. Luca Del Zanna | Università degli Studi di Firenze, Itàlia | 2011-06-20 | In this talk I will briefly describe our numerical models for two different classes of Astrophysical sources of high-energy radiation: namely Pulsar Wind Nebulae and (long) GRB projenitors in the magnetar scenario. Under some respects, in spite of many differences, these two objects may share some common physics, especially the magnetic mechanism needed to collimate the polar relativistic jets. I will also discuss the plasma diagnostic techniques that we use to infer non-thermal emission (in the case of PWNe) and some recent important observations in the gamma rays. Finally, and only under request!, I will briefly summarize the main features and the latest developments of the GRMHD code ECHO employed for the simulations. |
| Rapidly Rotating Black Holes through Gravitational Collapse | Motoyuki Saijo | Department of Physics, Rikkyo University, Japó | 2011-02-24 | We all believe that there exist various mass range of black hole in Nature. Some of them are produced through the binary merger of compact objects, while some others through gravitational collapse. Here I will focus on the collapse of a massive object to a massive black hole in order to investigate the properties of the rapidly rotating dynamic black holes. In this talk, I will focus on the new feature we found, the existence of quasi-periodic waves after the black hole ringdown in gravitational waveform. The radiation may be detected in the future space-based detector LISA, which may tell us the environment of the massive object. |
| Parallel, grid-adaptive simulations of relativistic jets | Zakaria Meliani | Katholieke Universiteit Leuven, Bèlgica | 2010-11-18 | The two types of Fanaroff-Riley radio loud galaxies, FRI and FRII, exhibit strong jets but with different properties. These differences may be associated to the central engine and/or the external medium. In this seminar I will present two models. I will start to discuss the dichotomy FRI/FRII accroding to the properties of the central engine, In this model we linked the AGN classification FRI and FRII to the transverse stratification of the jet. Indeed, theoretical arguments support this transverse stratification of jets with two components induced by intrinsic features of the central engine (accretion disk + black hole). We demonstrate that two-component jets with a relatively low kinetic energy flux contribution from the outer disk-jet are subject to the development of a relativistically enhanced, rotation-induced Rayleigh-Taylor type non-axisymmetric instability. This instability induces strong mixing between both components, decelerating the inner jet and leading to overall jet decollimation. In the second part, I will present the model that we proposed to explain HYbrid MOrphology Radio Sources (HYMORS), thereby invoking density discontinuities and variation in the initial open angle of jet. We explore how one-sided jet deceleration and a transition to FR I type can occur in HYMORS, which start as FR II (and remain so on the other side). The result of these work is that the FRII/FRI transition, can be associated to the central engine that induces transverse stratification of the jet and/or can be associated to the central engine (jet open angle) + external medium (density jump). |
| Supermassive black holes and relativistic jets in active galaxies | Andrei Lobanov | Max-Planck-Institut für Radioastronomie, Bonn, Germany | 2010-11-12 | Active galactic nuclei (AGN) powered by accretion of matter onto supermassive black holes (SMBH) are the most powerful sources of energy in the Universe. The bulk of this energy is channeled through broad-band emission and collimated outflows (jets). Relativistic jets, formed in the vicinity of central SMBH in AGN, show ample evidence connecting them to physical conditions in the AGN, particularly in the accretion disc and broad-line region. Imaging and polarimetry of radio emission from relativistic jets on finest angular scales provided by radio interferometry offers a range of possibilities for studying extreme vicinity of SMBH. This provides an excellent tool for probing the physical conditions in the extreme vicinity of SMBH and in the nuclearregions of active galaxies. Very long baseline interferometry (VLBI) experiments at millimetre wavelengths and with ground-space interferometers approach now a resolution sufficient to image the event horizon scales in the SMBH of the Milky Way and nearby galaxies. Recent results and prospects of studies of supermassive black holes and their vicinity with millimetre VLBI and space VLBI experiments will be discussed, with particular focus brought on detecting general relativity effects in the immediate vicinity of SMBH and answering the fundamental question of the physical nature of the central massive objects in galaxies. |
| Polarisation observations of Compact Steep Spectrum Sources at sub-arcsecond resolution | Franco Mantovani | Istituto di Radioastronomia - INAF, Bologna, Italy | 2010-11-08 | Measurements of the polarised emission from Compact Steep-Spectrum (CSS) sources can provide important information about the physical conditions inside and around the region of radio emission. CSS sources are physically small objects with radio sizes smaller than 15 kpc that reside inside their host galaxies. The most widely accepted interpretation is that CSS galaxies are young radio sources of ages < 10^6 yr. The measurement of the physical properties of CSS sources can provide insight into the conditions at the birth of a powerful radio source and those of sources developing in dense interstellar environments. An effect on the synchrotron polarised emission produced by this magnetized thermal plasma is Faraday rotation, which is proportional to the product of electron density and the magnetic field component parallel to the direction of propagation integrated along the line of sight. The magnetized plasma responsible for Faraday rotation and depolarisation can be situated either within the source, in a foreground screen, or in both. However, there are several indications, such as the magnitudes of the RMs, the total rotation of the electric vector position angle > 90 deg without very high depolarisation, that most of the observable effects are not internal to the source, but are produced in foreground material in the vicinity of the radio synchrotron source. A model to describe the depolarisation behaviour in external screens has been discussed by Burn (1966) and later generalized by Tribble (1991). Many CSS sources have been observed mainly with radio interferometers like the VLA and the VLBA. Our investigations have provided very interesting results about the polarised state of the radio emission CSS sources. |
| A new sample of faint blazars | Franco Mantovani | Istituto di Radioastronomia - INAF, Bologna, Italy | 2010-11-04 | The available blazar samples were selected at relatively high limiting flux densities in the radio and X-ray band. Those samples have small sizes (30-50 objects) making it difficult to statistically derive parameters related to beaming effects. Moreover, the estimate of those parameters is based on bright and intrinsically luminous sources. A deeper, larger sample of blazars has been constructed by Perlman et al. (1998) and by Landt et al. (2001): the "Deep X-ray Radio Blazar Survey". The DXRBS sample is currently the faintest (down to ~ 50 mJy at 5 GHz and power ~ 10^(24) W/Hz and largest blazar sample with nearly complete optical identifications. We have built a complete sample of 103 DXRBS sources selecting those with declination > -20 deg. It is expect that the objects in the DXRBS will be the counterparts of gamma-ray sources detected by the Fermi gamma-ray Observatory. After 1 year of Fermi observations, nearly 10% of the DXRBS sources in our sample have already been detected. In this presentation we will report on: - the structure of the sources observed so far with the European VLBI Network at 6cm - the results from Effelsberg 100-m telescope simultaneous multi-frequency observations (at 11cm, 6cm, 3.6cm, 2.8cm) to obtain properly measured spectral index, polarisation properties, and check for flux density variability. |
| X-ray Observations of Accreting Black Holes | Moritz Böck | Bamberg Observatory, University of Erlangen-Nuremberg, Germany | 2010-10-27 | X-ray observations are essential for studying accretion by compact objects. To understand the processes in the vicinity of accreting black holes, the spectral and temporal analysis of their X-ray emission is crucial. Studies of Active Galactic Nuclei and Galactic black holes are complementary. The analysis of the extragalactic source NGC 1052 is presented and a transition between spectral states of the bright Galactic X-ray source Cygnus X-1 is discussed. |
| The distribution of stars around massive black holes in galactic nuclei - Implications for extreme-mass ratio inspirals and LISA | Pau Amaro-Seoane | Max-Planck Institut für Gravitationsphysik (Albert Einstein-Institut), Potsdam, Alemanya | 2010-10-21 | Mass segregated stellar cusps are the natural configuration for nuclear stellar clusters in steady state with a central massive black hole of mass Mbh <~ few x 10^6 Msun. Detailed N-body and Fokker-Planck studies agree quite well with each other in the description of the bulk properties of the stellar distribution of such systems. For typical initial mass functions, the cluster is in the regime of strong mass segregation and therefore stellar-mass black holes dominate the spatial density in the innermost regions close to the massive black hole. As a natural consequence, the rates of extreme mass ratio inspirals detectable by LISA will be dominated by the inspiral of stellar-mass black holes. |
| Solar Wind Interaction with the Local Interstellar Medium: Achievements and Challenges | N. V. Pogorelov | Physics Department and Center for Space Plasma and Aeronomic Research University of Alabama in Huntsville, USA | 2010-10-18 | From the astrophysical perspective, the solar wind (SW) interaction with the local interstellar medium (LISM) is a particular case of the flow around an ejecting star placed into surrounding medium. I will describe the mathematical and physical statements of this problem and demonstrate how the interstellar magnetic field shapes the astropause. While the Voyager 1 and 2 spacecraft are exploring the boundaries of the heliosphere, our newest spacecraft, the Interstellar Boundary Explorer (IBEX) has started exploring the outermost reaches of the heliosphere, but from an orbit at 1 AU measuring the fluxes of energetic neutral atoms (ENAs) created in the boundary regions separating the heliosphere from the LISM. The first IBEX results revealed a sky-spanning ribbon of unexpectedly intense emissions of ENAs that had not been predicted previously by any physical model. For the next 5-10 years, heliophysics research is faced with an extraordinary opportunity that cannot be soon repeated. This is to make in situ measurements of the SW from the Sun to the heliospheric boundaries and, at the same time, extract information about the global behavior of the evolving heliosphere through ENA observations by the IBEX. In this talk, the effects are described of unsteady SW and interstellar magnetic field (ISMF) pressure of the shape of the heliopause and the terminations shock. We analyze the ISMF influence on the deflection of the neutral hydrogen flow in the inner heliosphere from its original direction in the unperturbed LISM and on the position of the ENA ribbon. It is shown that the ISMF direction strongly correlates with the ribbon location, which is useful for constraining the properties of the interstellar medium in the immediate vicinity of the heliospheric boundary". |
| Resolving the atmospheres of AGBs with IR-interferometry | Ivan Martí-Vidal | Max Planck Institut für Radioastronomie, Bonn, Germany | 2010-09-09 | Most of the stardust in the interstellar medium (ISM) comes from the dense stellar winds of Assymptotic Giant Branch (AGB) stars. The mechanism of this wind is not well understood yet. I will shortly discuss on the existing models of AGB atmospheres and winds and the problems of these models to explain the current spectroscopic and interferometric (high spatial-resolution) observations. I will finally report on new observations of a semi-regular AGB in the near-IR with the AMBER detector at the Very Large Telescope Interferometer (VLTI). A short technical description of this detector and the calibration/reduction procedure will be presented. Our observations cannot be explained with the current stellar models unless we use a mass much lower than predicted by stellar evolution and/or assume an ad-hoc warm molecular outer envelope. This would be the first spectro-interferometric evidence of an extended molecular layer around a semi-regular AGB star, and would be placed somewhere between the warm photosphere and the base of the dust-driven stellar wind. |
| Understanding the ultrafast TeV Variability from blazars | Dimitrios Giannios | Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, USA | 2010-06-30 | Recently two blazars (PKS 2155-304 and Mrk 501) have exhibited TeV flaring on timescales 1-2 orders of magnitude shorter that the light-crossing time of the host black holes. I discuss how these observations challenge our current paradigm for blazar emission and indicate that jet instabilities are the source of the ultrafast variability. A model of reconnection minijets forming inside the jet will be presented for the blazar variability. |
| Cosmic-Ray driven dynamo in galactic disks | Michal Hanasz | Centre for Astronomy, Nicolaus Copernicus University, Torun, Polònia | 2010-06-24 | I am going to present recent developments of local and global, galactic-scale numerical models, of the Cosmic-Ray driven dynamo, which was originally proposed by Parker (1992). We conduct global, galactic-scale CR-MHD numerical simulations of the dynamics of interstellar medium, composed of gas, magnetic-field, and cosmic-ray components. We take into account cosmic rays, accelerated in randomly distributed supernova remnants, and assume that supernovae deposit small-scale, randomly oriented, dipolar magnetic-fields into the ISM. We find that, the magnetization of galactic disks by exploding magnetized stars forms a favorable initial condition for the galactic dynamo process. The amplification timescale of the large-scale magnetic field, resulting from the CR-driven dynamo, is comparable to the galactic rotation period. The process converts efficiently small-scale magnetic fields of SN-remnants into the galactic-scale magnetic fields. The resulting magnetic-field structure resembles the observed X-shaped magnetic fields in edge-on galaxies. |
| Interfaces in Numerical Relativistic Hydrodynamics | Dr. Stephen Millmore | School of Mathematics, University of Southampton, England | 2010-06-17 | Current non-linear numerical simulations of neutron stars use single component models. However, evidence suggests that there are several different regions present within a neutron star. Qualitatively different behaviour is expected to occur within these regions and can be characterised by the equation of state. Problems arise when modelling a single component neutron star with a spatially varying equation of state, due to instabilities in the numerical methods. An alternative method of dealing with these regions is to use a multicomponent model. In such a case, level set methods can be used to track the interface between components. Boundary conditions must then be chosen and imposed at any interfaces to model the interaction between the fluid components correctly. Such techniques have been used with success in Newtonian computational fluid dynamics. Here I shall present an extension of these techniques to relativistic situations, and construct a simple multicomponent star model in general relativity by applying this extension. I then will provide some insight into the extension of these techniques for multidimensional situations. |
| AGN jet cores from radio to gamma-rays | Y. Y. Kovalev | Astro Space Center of Lebedev Physical Institute, Moscow, Russia | 2010-06-09 | Early results from the Fermi Gamma-ray Space Telescope have triggered multi-band radio-to-gamma-ray studies of AGN jets. In this talk, I will discuss recent results of our analysis of gamma-ray bright blazars, connection between emission mechanisms in radio domain and gamma-rays as well as localization of the site of gamma-ray emission. A study of synchrotron opacity with VLBI at different radio frequencies will be also presented and applied to estimate characteristics of opaque parsec-scale radio cores including the time delay associated with propagation of a perturbation in the core. |
| Kinematics of Relativistic Jets in Active Galactic Nuclei at Parsec Scales | Y. Y. Kovalev | Astro Space Center of Lebedev Physical Institute, Moscow, Russia | 2010-06-03 | I present recent results of a study of parsec-scale relativistic jets in Active Galactic Nuclei on the basis of a large VLBI monitoring program at 15 GHz (MOJAVE). I will discuss kinematics of compact Doppler-boosted jets including apparent jet acceleration measurements. Results and future prospects of a dedicated sub-parsec-scale study of the inner jet in the galaxy Virgo A will be also presented. The talk will be concluded by presenting the current status of the Space VLBI project Radioastron and new opportunities for AGN jet studies which will be opened by this mission. |
| Influence of self-gravity on the runaway instability of black hole-torus systems | Pedro Montero | Max-Planck-Institut für Astrophysik, Garching, Deutschland | 2010-05-19 | Results from the first fully general relativistic numerical simulations in axisymmetry of a system formed by a black hole surrounded by a self-gravitating torus in equilibrium are presented, aiming to assess the influence of the torus self-gravity on the onset of the runaway instability. We consider several models with varying torus-to-black hole mass ratio and angular momentum distribution orbiting in equilibrium around a non-rotating black hole. The tori are perturbed to induce the mass transfer towards the black hole. Our numerical simulations show that all models exhibit a persistent phase of axisymmetric oscillations around their equilibria for several dynamical timescales without the appearance of the runaway instability, indicating that the self-gravity of the torus does not play a critical role favoring the onset of the instability, at least during the first few dynamical timescales. |
| Exploring binary-neutron-star-merger scenario of short-gamma-ray bursts by gravitational wave observation | Kenta Kiuchi | Yukawa Institute for Theoretical Physics, Kyoto, Japan | 2010-05-18 | We elucidate the feature of gravitational waves from binary neutron stars merger collapsing to a black hole by general relativistic simulation. We show that GW spectrum imprints the coalescence-dynamics, formation process of disk, equation of state for neutron stars, total masses, and mass ratio. A formation mechanism of the central engine of short-gamma-ray bursts, which are likely to be composed of a black hole and surrounding disk, therefore could be constrained by GW observations. |
| The Local Group as a Dark Matter Laboratory | Jorge Peñarrubia | Institute of Astronomy, Cambridge University, Regne Unit | 2010-05-04 | The Local Group (the Milky Way, Andromeda and their satellite galaxies) will ever be the galactic system with the largest and most thorough observational data set in the Universe. The potential information that can be inferred on galaxy formation processes and on the nature of Dark Matter is indeed extraordinary and will strongly increase in the next few years thanks to the advent of large ground-based surveys of the Local Group (e.g. Pan-STARRS, LSST), as well as of spatial missions like GAIA and JWST. In this talk I will provide a state-of-the-art review of the available constraints on the amount and distribution of dark matter in many of the the Local Group members, as well as of the many implications that these results have on the present cosmological paradigm of galaxy formation and evolution (Cold Dark Matter, CDM). |
| Galaxy Evolution COde - A new semi-analytical model of galaxy formation | Elena Ricciardeli | Instituto de Astrofisica de Canarias | 2010-04-27 | I will present a new semi-analytical model of galaxy formation, GECO (Galaxy Evolution COde), aimed at a better understanding of when and how the two processes of star formation and galaxy assembly have taken place, by comparison with a wide variety of recent data. I will introduce the basis of the semi-analytical approach and the baryonic physics - gas cooling, star formation, feedback - included in the model. Then, I will show the ability of the model in reproducing both local boundary conditions, such as the local stellar mass function, and high-redshift data, focusing in particular on the time-scales of stellar formation and mass assembly, as constrained by near and far-IR surveys. |
| Numerical Relativity: Solving the issues in general relativity | Prof. Masaru Shibata | Yukawa Institute for Theoretical Physics, Kyoto University, Japan | 2010-03-31 | The next decade will be an exciting epoch in the field of general relativity: Gravitational-wave detectors will directly detect gravitational waves for the first time, and subsequently clarify coalescing mechanism of binary compact objects such as binary neutron stars and formation mechanism of black holes. Simultaneous detection of gravitational waves and electromagentic waves may determine the central engine of gamma-ray bursts (GRBs). Mechanism of supernova may be constrained if gravitational waves from it are detected. Numerical relativity plays an important role for theoretically predicting gravitational waveforms and mechanism of general relativistic astrophysical phenomena such as GRBs. I will review the perspective of the field of gravitational waves, and also talk the current activity of numerical relativity. |
| Solving Conservation Law and Balance Equations by Particle Management | Dr. Yossi Farjoun | Gregorio Millan Institute of Fluid Dynamics, Nanoscience and Industrial Mathematics, Universidad Carlos III de Madrid (Campus de Excelencia) | 2010-03-26 | Conservation equations are at the heart of many interesting and important problems. Examples come from physics, chemistry, biology, traffic and many more. Analytically, hyperbolic equations have a beautiful structure due to the existence of characteristics. These provide the possibility of transforming a conservation PDE into a system of ODE and thus greatly reducing the computational effort required to solve such problems. However, even in one dimension, one encounters problems quickly. The most obvious difficulty that needs to be dealt with has to do with the creation of shocks, or in other words, the crossing of characteristics. With a particle based method one would like to avoid a situation when one particle overtakes a neighboring one. However, since shocks are inherent to many hyperbolic equations and relevant to the problems that one would like to solve, it would be good not to 'smooth away' the shock but rather find a good representation of it and a good solution for the offending particles. In this talk we will discuss a new particle based method for solving (one dimensional, scalar) conservation law equations. The guiding principle of the method is the conservative property of the underlying equation. The basic method is conservative, entropy decreasing, variation diminishing and exact away from shocks. A recent extension allows solving equations with a source term, and another provides 'exact' solutions to the PDE. The method compares favorably to other benchmark solvers, for example CLAWPACK, and requires less computation power to reach the same resolution. A few examples will be shown to illustrate the method, and some of its extensions. Due to the current limitation to 1D scalar, the main application we are looking at is traffic flow on a large network. Though we still hope to manage to extend the method to either systems or higher dimensions (each of these extensions has its own set of difficulties), I would be happy to discuss further possible applications or suggestions for extensions. |
| High resolution studies of AGN: CTA102 and others | Christian M. Fromm | Max-Planck-Institut fuer Radioastronomie, Bonn, Alemanya | 2010-03-03 | Important information can be obtained from radio observations of active galactic nuclei (AGN), including single-dish light-curve analysis and multi-frequency very-long-baseline interferometry (VLBI) observations. We will present our study of the historical 2006 radio flare in the radio source CTA 102, where the shock-in-jet model and the hypothesis of an over-pressured jet during this flare were tested. For our analysis, we used single-dish observations as well as three multi-frequency VLBI observations. From the light curve analysis we identify the three different radiation loss stages, where the synchrotron stages shows a unexpected double peak structure. The evolution of the spectral parameters along the jet during the flaring event are extracted from VLBI observations and confirm our assumed model. The double peak structure can be explained by a change in the viewing angle and leads to a Doppler boosting of the flux densities around 2006.1. Prospectives of numerical simulations and studies on another sources will be presented as well. |
| ALMA: Observing the Cold Universe | Robert Laing | European Southern Observatory | 2009-12-11 | ALMA, the Atacama Large Millimetre/Sub-millimetre Array, is the largest current project in ground-based astronomy. It is an aperture synthesis array, optimized for high frequencies and currently under construction at a high, dry site in the Atacama desert of Northern Chile. When complete, it will provide unprecedented sensitivity, spatial resolution and imaging fidelity over the frequency range from 30 - 950 GHz. I will describe the key scientific goals of the project and outline its technical design. Interferometric observations with the first two ALMA antennas have recently been made, and construction is progressing rapidly. I will give an update on the current status and preparations for Early Science. |
| M87: A Laboratory for Astrophysical Processes | Philip E. Hardee | University of Alabama | 2009-12-10 | The accretion of matter onto a massive black hole is believed to feed the relativistic plasma jets found in many active galactic nuclei (AGN). Some AGN accelerate particles to energies exceeding 10^{12} electron Volts (eV) and are bright sources of very-high-energy (VHE) gamma-ray emission. However, it is not yet known where the VHE emission originates or what provides the mechanism for particle acceleration to very high energies. Firstly I report on radio and VHE observations of the radio galaxy M 87 that reveal a period of extremely strong gamma-ray flares accompanied by a strong increase in the radio flux. The results imply that particles must be accelerated to very high energies in the immediate vicinity of the black hole. Secondly I present new numerical simulation studies of the current driven instability (CDI) that could provide conversion of magnetic energy to plasma jet bulk kinetic energy and could also provide particle acceleration to the very high energies required by the observed emission. |
| Stellar density and kinematics in the central parsec of the Galaxy | Dr. Rainer Schödel | Instituto de Astrofísica de Andalucía | 2009-11-27 | The center of the Milky Way is a unique laboratory to study the structure and dynamics of a dense stellar cluster surrounding a massive black hole. At the Galactic center, we find the combination of nuclear cluster plus central black hole that is typical for spiral galaxies. While we can only study the integrated light in the case of the barely resolved extragalactic nuclear star clusters, the Milky Way is currently the only case, in which the structure of the cluster can be analyzed in detail, i.e. both stellar densities and dynamics can be probed directly, via measurements on individual stars. In this talk we will focus on recent research on the Milky Way nuclear star cluster. Recent measurement of stellar dynamics out to a projected distance of 1 pc from the black hole have lead to the first direct measurement of the enclosed extended, i.e. non-black hole, mass in the central parsec. We have also identified the reason why the black hole mass was underestimated by a factor of ~2 before orbital measurements became available. Perhaps one of the greatest current enigmas is the absence of a stellar cusp around the black hole. While a cusp is a solid prediction from theory, recent observations confirm that it is absent, at least in the stellar population that can be analyzed with current instrumentation. We will discuss the currently suggested explanations for this finding. |
| En el fondo del pozo de potencial: el centro de la Vía Láctea visto en el infrarrojo | Dr. Rainer Schödel | Instituto de Astrofísica de Andalucía | 2009-11-26 | El centro de la Vía Láctea se encuentra a sólo 26000 años luz del sistema solar, 100 veces más cerca que el núcleo de la próxima galaxia similar a la nuestra y 1000 veces más cerca que el próximo núcleo galáctico activo. Por esto, el centro de nuestra Galaxia es un laboratorio único para investigar los procesos fisicos en el fondo de potencial de una galaxia espiral común. En su camino hacia el Sistema Solar, la radiación emitida en el centro tiene que atravesar las densas nubes de polvo y gas en el plano de la Galaxia y es consecuentemente sujeto a una fuerte extinción. Por esto no es posible observar el centro de la Vía Láctea en luz visible, sólo en radio, infrarrojo y rayos X. En esta charla voy a presentar los resultados de investigaciones del centro Galáctico en el infrarrojo, con particular énfasis en el cúmulo estelar central y el agujero negro masivo, Sagitario A*, ubicado en el centro mismo de la Galaxia. |
| Aplicaciones de CMMR (Cabezas-Martín-Molina-Ruíz): una métrica global, analítica y aproximada | Javier E. Cuchi | Departamento de Física Fundamental, Área de Física Teórica, Universidad de Salamanca | 2009-10-30 | El método de Cabezas, Martín, Molina y Ruíz (CMMR) permite obtener soluciones analíticas globales para fuentes de fluido perfecto aisladas, estacionarias, y en rotación rígida. Para ello se parte de una doble aproximación: post-minkowskiana por una parte y de rotación lenta por otra. Dentro de este esquema se pueden construir y enlazar las soluciones interna y externa a la fuente, obteniendo asi una solución global. Las métricas así obtenidas tienen varias utilidades. En concreto, se mostrará cual es el procedimiento de cálculo para un fluido con ecuación de estado $mu+(1-n)p=cte$ y como se puede utilizar para demostrar que la métrica de Wahlquist no puede corresponder a una fuente aislada e identificar su oscuro parámetro $r_0$ así como que un fluido de estas características no puede ser fuente de Kerr. |
| Non-thermal emission associated to massive stars | Valentí Bosch-Ramon | Universitat de Barcelona/Max-Planck-Institut für Kernphysik | 2009-10-07 | Massive stars are strongly linked to the production of non-thermal emission. The strong winds produced by massive stars feed with matter the accretion process and can lead to the generation of jets, which are detected in radio and also emit high-energy photons. In addition, powerful collimated outflows from massive protostars interacting with the ISM can lead to the acceleration of particles and subsequent non-thermal emission from radio to high energies. Finally, shocks linked with the stellar wind in binary systems, either formed by two massive stars or by a massive star plus a young pulsar, can lead to the production of broadband non-thermal radiation. In this talk, I will briefly describe the sources and go through the most relevant mechanisms of non-thermal emission in which massive stars are involved. |
| Wonders of Astrometry. Space and ground based astrometry for the next decade | Guillem Anglada-Escudé | Dept. of Terrestrial Magnetism/Carnegie Institution of Washington, NASA Astrobiology Fellow | 2009-09-29 | Astrometry is the branch of astronomy which measures the motion of astronomical objects on the celestial sphere. I'll make a short historical introduction to astrometry and describe the observables that can be measured with the new generation of space astrometry missions in the optical (Gaia and SIM) with special enphasis on extrasolar planet detection capabilities around nearby stars. I'll also discuss the kind of astrometric measurements that can be done from the ground and their applications. I'll use as an example some of the projects in which I'm involved in the context of the Carnegie Astrometric Planet Search. |
| Stellar and planetary applications of stability in the three-body problem | Gareth Kennedy | Institut de Ciencies del Cosmos, Universitat de Barcelona | 2009-09-24 | The importance of stability in the three-body problem will be discussed in the context of three physical applications. Specifically the destruction of globular clusters as the orbit the galaxy; the disruption of stellar binaries by the massive black hole in the centre of the Milky Way; and a new method for discovering low mass extrasolar planets which are not detectable using available methods. This work was carried out during my PhD candidature at Monash University (Melbourne, Australia) based on a new formulism developed by Rosemary A. Mardling that predicts the long-term stability of three-body problem systems. This formulism predicts systems that are unstable to the eventual escape of one of the masses in a random walk process and can be applied to the general three-body problem." |
| Free-floating superJupiters | Prof. Rafael Rebolo | Instituto de Astrofísica de Canarias | 2009-09-15 | There is increasing evidence that objects with just a few times the mass of Jupiter populate star forming regions. I will review the current status of the research on these objects and the efforts to quantify the number density of free-floating super-Jupiters and identify their formation mechanism. |
| Near-Field Cosmology, a theoretician's point of view | Alexander Knebe | Universidad Autonoma de Madrid | 2009-06-16 | The quantitative mastery of cosmology and galaxy formation is targeted from two opposite directions: while observers use telescopes of ever growing size to look back in time theoreticians model cosmic structure formation and evolution from a period shortly after the big bang forward in time until today. But only recently it became possible for self-consistent cosmological simulations to make credible predictions for galaxies and their properties that can be directly compared to objects in the local Universe where observations are most complete and reliable. In this talk I will introduce you into this exiting discipline referred to as ""Near-Field Cosmology"" that gauges cosmology on small scales. After a short primer on computational cosmology I am going to present some of my recent research highlights regarding the dynamics of satellite galaxies as derived from such simulations of cosmic structure formation. |
| The co-evolution of galaxies and their super-massive black holes: view from the Sloan Digital Sky Survey | Guinevere Kauffmann | Max-Plank-Institut für Astrophysik, Garching, Alemanya | 2009-04-07 | The speaker will summarize recent investigations into the relation between the evolution of black holes and galaxies based on optical spectra from the Sloan Digital Sky Survey. |
| Quantum spacetime and the big bounce: an introduction to Loop Quantum Cosmology | Tomasz Pawlowski | Instituto Estructura de la Materia (CSIC) | 2009-04-01 | In the last few years the studies of simple cosmological models within Loop Quantum Cosmology have provided a qualiatively new picture of possible evolution of the universe, predicting in particular big bounce and the existence of a large universe preceeding ours. During this seminar I will present a short introduction to the main ideas behind the theory, its methods and main predictions, focusing in particular on the issue of singularity resolution and the dynamical predictions. |
| Understanding extragalactic jets from theory and observations | Manel Perucho Pla | Departament d'Astronomia i Astrofísica, Universitat de València | 2009-02-12 | I will review some aspects of my three years of research in the Max-Planck-Institut. These include modelling of extragalactic jets using numerical codes, stability theory and VLBI observations. In particular, I will report about a) results on evolution of components in the jet of the radio-galaxy 3C111 from the point of view of relativistic hydrodynamics, b) the observable effects of growing instabilities in jets as shown by detailed analysis of VLBI images of the jet in the quasar 0836+710, and c) I will present a new, fully parallelised, 3D relativistic hydrodynamics numerical code, along with the first results it has produced. These include the confirmation of the growth of resonant Kelvin-Helmholtz modes in sheared relativistic flows that can contribute to long term jet stabilization, as it was predicted from 2D simulations and KH stability theory. |
