Relativistic Astrophysics

Relativistic Astrophysics is the field of astrophysics dealing with compact objects such as neutron stars (NS) and black holes (BH). The study of its different areas, such as High-Energy Astrophysics or GW Astronomy, relies on the Theory of Relativity, either Special or General, and requires solving the relativistic magneto-hydrodynamic (MHD) equations for the matter and magnetic fields, Einstein's field equations for a dynamical gravitational field, and transport equations for neutrinos and EM radiation. High energy radiation is emitted in regions of strong gravitational fields near compact objects. A general relativistic description is necessary to describe the gravitational collapse of massive stars to NS or BH or compact binary coalescences (CBC) such as binary black hole (BBH) mergers or binary neutron star (BNS) mergers. These systems are sources of copious GW and are regarded as progenitors of the central engines that power high-energy events, such as gamma-ray bursts (GRBs), X-rays, and kilonova signals. Astronomers have long been investigating these systems using the complete frequency range of the electromagnetic spectrum and, nowadays, they have become the main targets of ground-based interferometers of GW, such as Advanced LIGO, Advanced Virgo and KAGRA. Progress in Relativistic Astrophysics has traditionally been driven by the analysis of the data collected by EM highenergy telescopes and satellites. New facilities as GW detectors are already boosting this progress as well, and neutrino detectors will also likely contribute in the near future. On the other hand, another crucial tool is provided by the corresponding theoretical studies to explain those observations. Theoretical astrophysics relies on numerical simulations to improve our understanding of the dynamics of astrophysical systems. The continuous improvements in computing and software technologies make possible large scale numerical simulations within a relativistic framework. Our group has a long and successful track record on the study of relativistic astrophysical systems through supercomputing simulations, which has resulted in hundreds of publications, thousands of citations, and dozens of invited talks at international conferences. A particular active area of research of our group is the modelling and interpretation of relativistic jets. The origin of the emission from AGN jets and the effect on the host galaxy and its surroundings is a hot topic of research in extragalactic astrophysics. These relativistic outflows are only directly detectable via their observed radiation, while their true physical properties remain hidden. Currently, the most promising method to study these outflows is by performing MHD simulations in either special (RMHD) or general relativity, and computing the synthetic emission from the fluid, topics in which members of our group have been working for more than twenty-five years (Gómez et al. 1995, 1997, Martí et al. 1994, 1995, 1997). To this aim, the group has developed its own computational codes which nowadays include a three-dimensional relativistic hydrodynamics (3D-RHD) code (Ratpenat; Perucho et al. 2010c), an axially symmetric 2.5D-RMHD code (Martí 2015a,b), and a 3D-RMHD code (Lóstrego; López-Miralles et al. 2022) together with a series of ancillary simulation codes (one-dimensional RMHD code adapted for narrow, teady, relativistic magnetized flows, quasi-1D-RMHD; Fuentes et al. 2018, Komissarov et al. 2015), and dataanalysis nd visualization tools. We have also added hydrogen ionization/recombination plus radiation physics to our odes (Perucho et al. 2021). This will allow us to handle two-phase, inhomogeneous media and study the processes f ionization both by the thermal radiation generated at the accretion disc feeding the central engine, on the one hand, nd also shock ionization, on the other hand. Our codes are suitable to study any astrophysical scenario involving elativistic, magnetized outflows. In this respect, we will also apply them to study physical processes relevant to the volution, impact and radiative mechanisms in X-ray and gamma-ray binary stars, following previous works in this ield (e.g., Perucho et al., 2008, 2010b; Bosch-Ramon et al., 2012b, 2015; López-Miralles et al., 2022).

Extragalactic jets at pc scales

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Jets, stars and the host galaxy

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Relativistic Astrophysics

Extragalactic jets at pc scales

Jets, stars and the host galaxy

Extragalactic jets at kiloparsec scales

Relativistic flows in X-ray and Gamma-ray binary stars

Numerical Relativity - Formulations and methods

NR simulations of BNS mergers and post-merger HMNS remnants

Multimessenger aspects of NS crustal fracture and magnetars.

Ante interdum

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