Theoretical Black Hole Mass Distributions

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Abstract
We derive the theoretical distribution function of black hole masses by studying the formation processes of black holes. We use the results of recent 2D simulations of core-collapse to obtain the relation between remnant and progenitor masses and fold it with an initial mass function for the progenitors. We examine how the calculated black-hole mass distributions are modified by (i) strong wind mass loss at different evolutionary stages of the progenitors, and (ii) the presence of close binary companions to the black-hole progenitors. Thus, we are able to derive the binary black hole mass distribution. The compact remnant distribution is dominated by neutron stars in the mass range 1.2-1.6Msun and falls off exponentially at higher remnant masses. Our results are most sensitive to mass loss from winds which is even more important in close binaries. Wind mass-loss causes the black hole distribution to become flatter and limits the maximum possible black-hole mass (<10-15Msun). We also study the effects of the uncertainties in the explosion and unbinding energies for different progenitors. The distributions are continuous and extend over a broad range. We find no evidence for a gap at low values (3-5Msun) or for a peak at higher values (~7Msun) of black hole masses, but we argue that our black hole mass distribution for binaries is consistent with the current sample of measured black-hole masses in X-ray transients. We discuss possible biases against the detection or formation of X-ray transients with low-mass black holes. We also comment on the possibility of black-hole kicks and their effect on binaries.