Low-mass X-ray binaries from black-hole retaining globular clusters

TL;DR

This study models black hole low-mass X-ray binaries in globular clusters to understand their formation, population, and potential origins, revealing the influence of black hole retention on observable binary systems.

Contribution

It introduces a simulation framework for BH-LMXB formation in GCs, highlighting how black hole retention affects the number and properties of these binaries.

Findings

GCs with ~1000 BHs produce ~150 ejected BH-LMXBs

GCs with ~20 BHs produce no ejected BH-LMXBs

Identified five candidate BH-LMXBs possibly originating from GCs

Abstract

Recent studies suggest that globular clusters (GCs) may retain a substantial population of stellar-mass black holes (BHs), in contrast to the long-held belief of a few to zero BHs. We model the population of BH low-mass X-ray binaries (BH-LMXBs), an ideal observable proxy for elusive single BHs, produced from a representative group of Milky Way GCs with variable BH populations. We simulate the formation of BH-binaries in GCs through exchange interactions between binary and single stars in the company of tens to hundreds of BHs. Additionally, we consider the impact of the BH population on the rate of compact binaries undergoing gravitational wave driven mergers. The characteristics of the BH-LMXB population and binary properties are sensitive to the GCs structural parameters as well as its unobservable BH population. We find that GCs retaining $\sim 1000$ BHs produce a galactic population of $\sim 150$ ejected BH-LMXBs whereas GCs retaining only $\sim20$ BHs produce zero ejected BH-LMXBs. Moreover, we explore the possibility that some of the presently known BH-LMXBs might have originated in GCs and identify five candidate systems.