Ministry Project: PID2021-127495NB-I00
Funding Body: MICIN
Main Researchers: Miguel Ángel Aloy Torás, Martín Obergaulinger
Abstract:
After the core of a massive star has exhausted its nuclear fuel and can no longer support itself against gravity, it collapses to form a proto- neutron star (PNS). This stage opens several evolutionary paths: the core can produce i) a regular core-collapse supernova driven by interaction between neutrinos streaming out of the PNS and the surrounding gas, ii) a hypernova in which rotation and magnetic field provide additional energy input and drive fast, collimated outflows, or iii) it may fail to explode and leave behind a black hole instead of a neutron star (NS). While the dynamics in the interior of the cores are accessible only to multi-messenger signals of neutrinos and gravitational waves (GWs), the dying star can shine extremely bright in electromagnetic radiation for months before fading away. The SN expels heavy elements produced during the explosion and in the envelope of the progenitor star, in a complex geometry that depends on the conditions set during the explosion.
These events are at the crossroads of the disciplines of stellar evolution, general relativity fluid dynamics, high-energy astrophysics, and nuclear and particle physics. Thorough theoretical work is required to understand the conditions before the core of a massive star collapses, the processes in the engine launching the explosion, the dynamics of the ejected gas, the compact remnants they leave behind, the production of heavy elements, and the observable signals. This project will use a suite of numerical methods tailored to each of these aspects to look at supernovae from different, complementary angles and
advance our knowledge on how these phases are connected.
The assumptions of spherical symmetry and hydrostatic equilibrium made in stellar evolution, are no longer valid during the last phase before collapse. We will deal with deviations from that ideal state by evolving stellar cores in three-dimensional magnetohydrodynamic simulations in the last minutes before the onset of collapse. The goal is to assess how convection, rotation and magnetic fields during this phase affect the conditions determining whether an explosion takes place and what kind of remnant will be produced. The end points of these models (followed to the onset of collapse) will serve as consistent initial 3D models for ensuing collapse and early post-collapse phase. From the onset of collapse, another set of numerical models including nuclear and neutrino physics, will focus on the few seconds after the formation of the PNS. These simulations will show how the magnetic fields of young NSs are determined, how jets are formed, and what the characteristics of the emitted neutrino and GW signals are. We will then employ methods adapted to follow the propagation of the ejected gas for years and study the morphology of the supernova, which can be compared to electromagnetic observations. For this purpose, and to determine the impact on the chemical evolution of the universe, we will calculate the nucleosynthetic yields of the explosions. Further information about the explosions will be gathered from the properties like internal magnetic fields and magnetospheres of the produced NSs. We will develop new numerical methods to deal with the complex physics at small scales that play a role in the transition from PNS to NS and model the emission of strongly magnetized NSs. Altogether, this set of post-collapse observables will help to unveil the type of stellar progenitor yielding them.
