The rate of binary black hole mergers inferred from Advanced LIGO observations surrounding GW150914

Abstract

A transient gravitational-wave signal was identified in the twin Advanced LIGO detectors on September 14, 2015 at 09:50:45 UTC (GW150914). To assess the implications of this discovery, the detectors remained in operation with unchanged configurations over a period of 39 d around the time of the signal. A search of 16 days of simultaneous two-detector observational data found GW150914 to have a false alarm probability (FAP) of 2×10−7. Parameter estimation followup on this trigger identifies its source as a binary black hole (BBH) merger with component masses (m1,m2)=36+5−4,29+4−4M⊙ at redshift z=0.09+0.03−0.04. Here we report on the constraints these observations place on the rate of BBH coalescences. Considering only GW150914, assuming that all BBHs in the universe have the same masses and spins as this event, imposing a false alarm threshold of 1 per 100 years, and assuming that the BBH merger rate is constant in the comoving frame, we infer a 90% credible range of 2−53Gpc−3yr−1 (comoving frame). Incorporating all triggers that pass the search threshold while accounting for the uncertainty in the astrophysical origin of each trigger, we estimate a higher rate, ranging from 6−400Gpc−3yr−1 depending on assumptions about the BBH mass distribution. All together, our various rate estimates fall in the conservative range 2−400Gpc−3yr−1.