Formation of black hole and accretion disk in a massive high-entropy stellar core collapse

TL;DR

This study presents the first fully general relativistic simulations of rotating high-entropy stellar core collapse, revealing black hole formation and diverse accretion disk structures influenced by initial rotation.

Contribution

It provides the first numerical results of axisymmetric GR simulations for high-entropy stellar core collapse, including microphysics and detailed disk formation dynamics.

Findings

Weak bounce leads to black hole formation.

Rotation influences disk geometry and convection.

Neutrino luminosity varies with convective activity.

Abstract

We present the first numerical result of fully general relativistic axisymmetric simulations for the collapse of a rotating high-entropy stellar core to a black hole and an accretion disk. The simulations are performed taking into account the relevant microphysics. We adopt as initial condition a spherical core with constant electron fraction ($Y_e = 0.5$) and entropy per baryon $s$ = 8 $k_B$, and angular velocity is superimposed. In the early phase, the core collapses in a homologous manner. Then, it experiences a weak bounce due to the gas pressure of free nucleons. Because the bounce is weak, the core collapses eventually to a black hole. Subsequent evolution depends on initial angular velocity. When the rotation is not fast, a geometrically thin (but optically thick) accretion disk is formed, and shock waves are formed in the inner part of the disk. For the moderately rotating case, the thin accretion disk expands eventually to be a geometrically thick torus after sufficient accumulation of the thermal energy generated at the shocks. Furthermore, convection occurs inside the torus. Neutrino luminosities vary violently with time because of the convective motion. For the rapidly rotating case, by contrast, a geometrically thick torus is formed soon after the black hole formation, and convective activity is weak due to the presence of epicyclic mode.