We review the formation scenarios for binary black holes, and show that their coalescence rate depends very strongly on the outcome of the second mass transfer. However, the observations of IC10 X-1, an binary with a massive black hole accreting from a Wolf-Rayet star proves that this mass transfer can be stable. We analyze the future evolution of IC10 X-1 and show that it is very likely to form a binary black hole system merging in a few Gyrs. We estimate the coalescence rate density of such systems to be 0.06Mpc−3Myr−1, and the detection rate for the current LIGO/VIRGO of 0.69yr−1, a much higher value than the expected double neutron star rate. Thus the first detection of a gravitational wave source is likely to be a coalescence of a binary black hole.
@article{arxiv.0907.5515,
title = {Observational evidence for stellar mass binary black holes and their coalescence rate},
author = {T. Bulik and K. Belczynski},
journal= {arXiv preprint arXiv:0907.5515},
year = {2009}
}