Kiril Maltsev (Germany)
kiril.maltsev @ h-its.org
Statistical stellar evolution and final fate forecasting
Stars are self-gravitating bodies that are massive enough to ignite nuclear fusion as they convert gravitational potential energy into thermal heat. They form through the gravitational collapse of gigantic gaseous nebula, and burn successively heavier elements as they undergo a sequence of evolutionary phases, governed by an exciting interplay of gravity and thermodynamics, nuclear and particle quantum physics, and hydrodynamics. Stars end their lives by transformation into compact objects, or in violent supernova (SN) explosions tearing them apart. Massive stars become large, shine bright, and die young.
Stars evolve on timescales that are orders of magnitude beyond human lifetimes. Therefore, the only way to probe stellar evolution models is to compare statistical model predictions with observations of stellar populations. Current population synthesis methods require an efficient yet reliable way to determine the outcome of stellar evolution. However detailed models such as MESA are computationally too expensive for generating predictions at scale over a wide and fine-grained parameter range. We propose a solution to this problem by constructing machine learning based stellar evolution emulators, which are trained on pre-computed evolutionary tracks, but have the capability to generalize.
There are two main astrophysical applications in which we make use of our emulation method. The first is the prediction of the statistical distribution of photometric observables of solar metallicity stars during more than 99% of their lifetimes (from zero age main sequence up to end of core helium burning), while covering the entire mass range from red dwarves to 300 solar mass Wolf-Rayet stars. The second is the prediction of final fates of massive stars that undergo iron core collapse. To this end, we formulate explodability criteria, which evaluate the pre-SN core structure at onset of collapse to predict whether the outcome will be a successful or a failed SN. We then relate these outcomes to stellar progenitor properties at the end of core helium burning, while taking into account differences in pre-SN structures between single- and binary stripped stars and as function of metallicity.
Related research projects concern the study of effects of variable convective core overshoot on the compact remnant mass landscape from massive single star evolution, the prediction of gravitational waves from neutron star merger remnants, and the question whether a gravitational singularity genuinely forms when iron core collapse results in a failed SN.
Supervisor: Friedrich Roepke (HITS)
