A Black-Hole Excision Scheme for General Relativistic Core-Collapse Supernova Simulations

TL;DR

This paper introduces a stable black-hole excision scheme for general relativistic supernova simulations, enabling long-term modeling of black-hole formation and fallback phenomena in stellar collapse scenarios.

Contribution

It presents a novel excision method compatible with constrained evolution schemes, including boundary conditions and hydrodynamics upgrades, for supernova simulations with relativistic effects.

Findings

Successfully simulated black-hole formation in a 85 solar mass star.

Extended simulation times past 9 seconds after black-hole formation.

Demonstrated two-dimensional fallback explosion simulation.

Abstract

Fallback supernovae and the collapsar scenario for long-gamma ray burst and hypernovae have received considerable interest as pathways to black-hole formation and extreme transient events. Consistent simulations of these scenarios require a general relativistic treatment and need to deal appropriately with the formation of a singularity. Free evolution schemes for the Einstein equations can handle the formation of black holes by means of excision or puncture schemes. However, in constrained schemes, which offer distinct advantages in long-term numerical stability in stellar collapse simulations over well above $10^{4}$ light-crossing time scales, the dynamical treatment of black-hole spacetimes is more challenging. Building on previous work on excision in conformally flat spacetimes, we here present the implementation of a black-hole excision scheme for supernova simulations with the CoCoNuT-FMT neutrino transport code. We describe in detail a choice of boundary conditions that ensures long-time numerical stability, and also address upgrades to the hydrodynamics solver that are required to stably evolve the relativistic accretion flow onto the black hole. The scheme is currently limited to a spherically symmetric metric, but the hydrodynamics can be treated multi-dimensionally. For demonstration, we present a spherically symmetric simulation of black-hole formation in an $85 M_\odot$ star, as well as a two-dimensional simulation of the fallback explosion of the same progenitor. These extend past 9s and 0.3s after black-hole formation, respectively.