On the coexistence of stellar-mass and intermediate-mass black holes in globular clusters

TL;DR

This study investigates the likelihood of stellar-mass black hole binaries co-existing with intermediate-mass black holes in globular clusters, using simulations and analytic methods to understand their formation, interactions, and implications for detecting IMBHs.

Contribution

It introduces a combined simulation and analytic approach to assess black hole binary formation and their impact on constraining the presence of IMBHs in globular clusters.

Findings

Detection of BH binaries can constrain IMBH presence in clusters.

Most BHs are ejected, leaving only the most massive BHs to form binaries with IMBHs.

Presence of BH binaries suggests IMBHs less massive than ~10^3 solar masses.

Abstract

In this paper, we address the question: What is the probability of stellar-mass black hole (BH) binaries co-existing in a globular cluster with an intermediate-mass black hole (IMBH)? Our results suggest that the detection of one or more BH binaries can strongly constrain the presence of an IMBH in most Galactic globular clusters. More specifically, the detection of one or more BH binaries could strongly indicate against the presence of an IMBH more massive than $\gtrsim 10^3$ M$_{\rm \odot}$ in roughly 80\% of the clusters in our sample. To illustrate this, we use a combination of N-body simulations and analytic methods to weigh the rate of formation of BH binaries against their ejection and/or disruption rate via strong gravitational interactions with the central (most) massive BH. The eventual fate of a sub-population of stellar-mass BHs (with or without binary companions) is for all BHs to be ejected from the cluster by the central IMBH, leaving only the most massive stellar-mass BH behind to form a close binary with the IMBH. During each phase of evolution, we discuss the rate of inspiral of the central BH-BH pair as a function of both the properties of the binary and its host cluster.