Compact Binaries in Star Clusters II - Escapers and Detection Rates

TL;DR

This paper investigates black hole binaries ejected from globular clusters, assessing their potential as gravitational wave sources detectable by ground-based and space-based detectors, and estimates detection rates and observability.

Contribution

It introduces a self-consistent Monte Carlo method to study ejected black hole binaries and evaluates their detectability by current and future gravitational wave observatories.

Findings

Many ejected binaries have short periods and merge within a Hubble time.

Estimated detection rate for ground-based detectors shows a modest increase over stellar evolution predictions.

Some binaries may be resolvable by LISA, especially at extragalactic distances.

Abstract

We use a self-consistent Monte Carlo treatment of stellar dynamics to investigate black hole binaries that are dynamically ejected from globular clusters to determine if they will be gravitational wave sources. We find that many of the ejected binaries have initially short periods and will merge within a Hubble time due to gravitational wave radiation. Thus they are potential sources for ground-based gravitational wave detectors. We estimate the yearly detection rate for current and advanced ground-based detectors and find a modest enhancement over the rate predicted for binaries produced by pure stellar evolution in galactic fields. We also find that many of the ejected binaries will pass through the longer wavelength Laser Interferometer Space Antenna (LISA) band and may be individually resolvable. We find a low probability that the Galaxy will contain a binary in the LISA band during its three-year mission. Some such binaries may, however, be detectable at Mpc distances implying that there may be resolvable stellar-mass LISA sources beyond our Galaxy. We conclude that globular clusters have a significant effect on the detection rate of ground-based detectors and may produce interesting LISA sources in local group galaxies.