Speaker
Description
There are multiple well-studied astrophysical pathways for producing stellar-mass black holes (BHs), and in this talk, I will focus on their formation channel through the failed explosion of collapsing iron cores in massive stars. At the end of core-silicon burning, massive stars develop a an electron-degeneracy supported iron core. The iron core loses stability when it surpasses its effective Chandrasekhar mass. The collapse of the iron-core may result in an explosion, observable as a Type II, Ib or Ic supernova (SN), powered by the neutrino heating mechanism. There are, however, theoretical as well as observational indications that this SN mechanism is not always successful - that iron-cores sometimes fail to explode and continue to fall in until a BH is formed. To discriminate the outcome (successful versus failed supernova), different “explodability” measures based on the stellar structure at the onset of iron-core infall have been introduced, which allow us to make statistical prediction of SN outcomes. The final fate landscape of stars undergoing iron-core collapse has been substantially revised over the past 20 years, and up-to-date the scientific community has not reached a consensus. I will argue that recent advances in the understanding of the late-phase evolution of massive stars as well as the trimodal peak-dearth structure in the low-mass end of the distribution of chirp masses of binary BHs observed by the LIGO-Virgo-KAGRA collaboration after the GWTC-4 gravitational wave data release strongly favour a bimodal pattern in the final fate landscape as a function of core mass.
In a general relativistic treatment of a failed SN, BH formation is typically associated with a singularity forming as matter continues to contract under its own gravity. I will address the question whether singularity prediction indicates a breakdown of General Relativity, while distinguishing between the geodesic incompleteness (GI) and infinite curvature (IC) singularity concepts. My answer will be yes for IC but no for GI. I will close with remarks concerning heat exchange with a quasi-static Schwarzschild BH and the validity of the four laws of thermodynamics.