First LIGO events: binary black holes mergings

Abstract

Based on evolutionary scenarios for binary stellar evolution we study the merging rates of relativistic binary stars (NS+NS, NS+BH, BH+BH) under different assumptions of BH formation. We find the BH+BH merging rate in the range one per 200,000 -- 500,000 year in a Milky-Way type galaxy, while the NS+NS merging rate $R_{ns}$ is approximately 10 times as high, which means that the expected event rate even for high mean kick velocities of NS up to 400 km/s is at least 30-50 binary NS mergings per year from within a distance of 200 Mpc. As typical BH is formed with a mass 3-10 times the NS mass (assumed 1.4 M$_\odot$), the rates obtained imply that the expected detection rate of binary BH by a LIGO-type gravitational wave detector is 10-100 times higher than the binary NS merging rate for a wide range of parameters.