Accreting black hole binaries in globular clusters

TL;DR

This paper investigates how mass-transferring black hole binaries form in globular clusters, showing they are dynamically created and can exist regardless of the total black hole population, challenging previous assumptions.

Contribution

It demonstrates that mass-transferring black hole binaries form dynamically in globular clusters across various properties, independent of the total black hole count.

Findings

Black hole binaries are formed through dynamical encounters.

Presence of such binaries does not correlate with total black hole number.

Detection of these binaries does not imply a large black hole population.

Abstract

We explore the formation of mass-transferring binary systems containing black holes within globular clusters. We show that it is possible to form mass-transferring black hole binaries with main sequence, giant, and white dwarf companions with a variety of orbital parameters in globular clusters spanning a large range in present-day properties. All mass-transferring black hole binaries found in our models at late times are dynamically created. The black holes in these systems experienced a median of $\sim 30$ dynamical encounters within the cluster before and after acquiring the donor. Furthermore, we show that the presence of mass-transferring black hole systems has little correlation with the total number of black holes within the cluster at any time. This is because the net rate of formation of black hole-non-black hole binaries in a cluster is largely independent of the total number of retained black holes. Our results suggest that the detection of a mass-transferring black hole binary in a globular cluster does not necessarily indicate that the host cluster contains a large black hole population.