Expected masses of merging compact object binaries observed in gravitational waves

Abstract

We use the well-tested STARTRACK binary population synthesis code to examine the properties of the population of compact object binaries. We calculate the distribution of masses and mass ratios, taking into account weights introduced by observability in gravitational waves during inspiral. We find that in the observability-weighted distribution of double neutron star binaries there are two peaks: one for nearly equal-mass systems, and one for systems consisting of a low- and a high-mass neutron star, q = 0.6-0.7. The observability-weighted distribution of black hole neutron star binaries is concentrated on systems with mass ratio q = 0.3-0.5, while for double black hole binaries the observability-weighted distribution is dominated by massive, nearly equal-mass binaries with q > 0.7.