Channels of Stellar-mass Black Hole Formation

On the basis of a large collection of detailed 3D core-collapse supernova simulations carried to late times, we identify four channels of stellar-mass black hole formation. Our examples for Channel 1 can involve the formation of black holes in energetic asymmetric supernova explosions. Our Channel 2 example involves a modest supernova explosion that nevertheless leaves behind a black hole. The latter may not be easily distinguishable from “standard” supernovae that birth neutron stars. Our Channel 3 example experiences an aborted core-collapse explosion, more often in the context of a low-metallicity progenitor, whose residue is a black hole with a mass perhaps up to ∼40 M_⊙. The latter may be accompanied by a pulsational pair-instability supernova. Channel 4 is the only quiescent or “silent” scenario for which perhaps ∼5-15 M_⊙ black holes are left. Where appropriate, we estimate ⁵⁶Ni yields, explosion energies, approximate recoil speeds, and residual black hole masses. The progenitor mass density and binding energy profiles at collapse influence the outcome in a systematic way. We speculate that the statistics and prevalence of these various channels depend not only on still evolving supernova theory, but on remaining issues with the theory of massive star evolution, binary interaction, wind mass loss, metallicity, and the nuclear equation of state. Importantly, we suggest, but have not proven, that the silent channel for black hole formation may not be the dominant formation modality.