Redshift Evolution of the Black Hole Merger Rate from Globular Clusters

Abstract

As the sensitivity of current and future gravitational-wave detectors improves, it will become possible to measure the evolution of the binary black hole merger rate with redshift. Here, we combine detailed fits to state-of-the-art dynamical models of binary black hole formation in dense star clusters with a cosmological model of cluster formation across cosmic time. We find a typical merger rate of 14 Gpc −3 yr −1 in the local universe, with a reasonable range of 4–18 Gpc −3 yr −1 , depending on the rate of cluster disruption and the cluster initial mass function. This rate increases by a factor of 6 to redshift z  = 2.7 before declining at higher redshifts. We compare the merger rate from binaries produced in clusters to similar estimates from isolated binaries and triples in galactic fields, and discuss various ways that these different formation channels could add up to the current merger rate observed by the Laser Interferometer Gravitational-Wave Observatory/Virgo.