Mass limits for black hole formation

We present a series of two-dimensional core-collapse supernova simulations for a range of progenitor masses and different input physics. These models predict a range of supernova energies and compact remnant masses. In particular, we study two mechanisms for black hole formation: prompt collapse and delayed collapse owing to fallback. For massive progenitors (greater than 20 M.), after a hydrodynamic time for the helium core (a few minutes to a few hours), fallback drives the compact object beyond the maximum neutron star mass, causing it to collapse into a black hole. With the current accuracy of the models, progenitors more massive than 40 M. form black holes directly with no supernova explosion (if rotating, these black holes may be the progenitors of gamma-ray bursts). We calculate the mass distribution of black holes formed and compare these predictions to the observations, which represent a small biased subset of the black hole population Uncertainties in these estimates are discussed.