ASTROPHYSICS

Supernovae of Type Ia are modeled as thermonuclear explosions of a carbon-oxygen white dwarf stars. The way these trigger the explosive burning, however, is still unclear. This project performs hydrodynamic simulations that give insights into possible explosion mechanisms. With its pipeline extending from explosion simulation to the derivation of synthetic observables, the project allows for a direct comparison with astronomical observations thus scrutinizing the modeled scenarios.

Traditionally, numerical simulations of core-collapse supernovae have been performed with spherically symmetric initial models for the progenitor stars, because stellar evolution is computed with this restriction. Recently, however, it has been demonstrated that pre-collapse asymmetries in the convectively burning oxygen shell can have an impact on the explosion by enhancing turbulence behind the supernova shock. In this project researchers simulated the final seven minutes of oxygen burning and the subsequent collapse of a 19 solar-mass star in order to investigate the consequences of pre-collapse asymmetries for the supernova explosion.

The "ray-by-ray" approximation is a widely used simplification of the time-dependent, six-dimensional transport of all neutrino species in core-collapse supernovae. It reduces the dimensionality of the computationally challenging problem by assuming that non-radial flux components are negligible. This leads to the solution of three-dimensional (radius-, energy-, and angle-dependent) transport equations for all angular directions of the spatial polar grid. Such a task can be extremely efficiently parallelized also on huge numbers of computing cores. In this project 3D simulations were performed to test this approximation and could demonstrate its validity.

Modern simulations of galaxy formation, which simultaneously follow the co-evolution of dark matter, cosmic gas, stars, and supermassive black holes, enable us to directly calculate the observable signatures that arise from the complex process of cosmic structure formation. TNG50 is an unprecedented ‘next generation’ cosmological, magneto-hydrodynamical simulation -- the third and final volume of the IllustrisTNG project. It captures spatial scales as small as ~100 parsecs, resolving the interior structure of galaxies, and incorporates a comprehensive model for galaxy formation physics.

Recently the first three-dimensional simulations have confirmed the long-standing hypothesis that the neutrino-driven mechanism, supported by violent hydrodynamic instabilities and turbulent mass flows, can explain supernova explosions of stars with more than 8−10 solar masses. Further consolidation of this mechanism and a deeper theoretical understanding of its functioning require the exploration of a broader variety of progenitor stars and of dependences on the initial conditions prior to iron-core collapse. In this Gauss project the influence of stellar rotation, perturbations in the convective oxygen-burning layer, and of large mass-infall rates due to high core compactness in very massive progenitor stars were explored.

First self-consistent, first-principle simulations in three dimensions have provided support for the viability of the neutrino-driven mechanism as an explanation of supernova explosions of stars with more than 8−10 solar masses. While these results respresent fundamentally important progress in our understanding of how massive stars terminate their lives, the enormous complexity and computational demand of the involved neutrino physics set severe resolution limitations to current full-scale supernova models. In this project, the numerical convergence of the present simulations were investigated.

Why do galaxies that live in the enormous structures known as galaxy clusters look different from normal, isolated galaxies, like our Milky Way? To answer this question, astrophysicists have created the Hydrangea simulations, a suite of 24 high-resolution cosmological hydrodynamical simulations of galaxy clusters. Containing over 20,000 cluster galaxies in unprecedented detail and accuracy, these simulations are giving astrophysicists a powerful tool to understand how galaxies have formed and evolved in one of the most extreme environments of our Universe.

A multi-million compute hours allocation by the Gauss Centre for Supercomputing on HPC system SuperMUC of the Leibniz Supercomputing Centre (LRZ) was used to carry out Aurora, a new set of radiation-hydrodynamical simulations of galaxy formation during reionization. Numerical simulations have emerged as the most powerful tools for the ab initio theoretical treatment of reionization. 

The Stellar Core-Collapse Group at the Max Planck Institute for Astrophysics (MPA) is able to conduct the presently most advanced 3D supernova simulations thanks to a suitably constructed description of the neutrino physics and a highly efficient, extremely well parallelized numerical implementation on petascale system SuperMUC. Because neither experiments nor direct observations can reveal the processes at the center of exploding stars, highly complex numerical simulations are indispensable to develop a deeper and quantitative understanding of this hypothetical “neutrino-driven explosion mechanism”, whose solid theoretical foundation is still missing.

Massive stars end their lives as core-collapse supernovae when the stellar core implodes to a neutron star and the stellar envelope is expelled. Using computer models, we have simulated the mixing processes occurring during the explosion without assuming any symmetry.