Compact binaries ejected from globular clusters as gravitational wave sources

Performing N-body simulations, we examine the dynamics of black hole–black hole (BH–BH) (10 M⊙ each) and neutron star–neutron star (NS–NS) (1.4 M⊙ each) binaries formed in a cluster and its implications for gravitational wave detection. A significant fraction of compact binaries are ejected from a globular cluster after core collapse. Among the total number of ejected compact objects, 30 per舁cent of them are in binaries. Merging time-scales of ejected binaries, which depend on the cluster's velocity dispersion, are in some cases shorter than the age of the Universe. During the merging event, these dynamically formed compact mergers are expected to produce gravitational waves that can be detectable by the advanced ground-based interferometers. Based on our reference assumptions, merger rates of ejected BH–BH and NS–NS binaries per globular cluster are estimated to be 2.5 and 0.27 per Gyr, respectively. Assuming the spatial density of globular clusters to be 8.4 h3 clusters Mpc−3 and extrapolating the merger rate estimates to the horizon distance of the advanced Laser Interferometer Gravitational Wave Observatory-Virgo network, we expect the detection rates for BH–BH and NS–NS binaries with cluster origin to be 15 and 0.024 yr−1, respectively. We find out that some of the dynamically formed binaries are ejected with a large escape velocity. They can be responsible for short gamma-ray bursts whose locations are far from host galaxies.