MOCCA-SURVEY Database I. Unravelling black hole subsystems in globular clusters

TL;DR

This study introduces a new method to identify and characterize black hole subsystems in globular clusters using observational data, revealing many clusters likely host hundreds of black holes with specific properties.

Contribution

It proposes a novel way to infer black hole subsystem sizes and densities in globular clusters from observational parameters, establishing a fundamental plane relation.

Findings

Many Milky Way GCs likely host hundreds of black holes.

Black hole subsystems have low typical densities around 10-10^5 Ms/pc^3.

Black holes in these systems have average masses between 14-22 solar masses.

Abstract

In this paper, we discuss how globular clusters (GCs) structural and observational properties can be used to infer the presence of a black hole system (BHS) inhabiting their inner regions. We propose a novel way to identify the BHS size, defined as the GC radius containing a mass contributed equally from stars and stellar BHs. Using this definition, similar to the well-known concept of "influence radius", we found a "fundamental plane" connecting the BHS typical density with the GC central surface density profile, total luminosity and observational half-mass radius. Our approach allows us to define a unique way to connect the observational GCs parameters with their dark content. Comparing our results with observed Milky Way GCs, we found that many of them likely host, at the present time, as many as several hundreds of BHs. These BHS are characterized by a relatively low typical density, $\rho_\bhs \sim 10-10^5\Ms$ pc$^{-3}$ and composed of relatively massive BHs, with average masses in the range $m_\bhs = 14-22\Ms$. We also show that a similar approach can be used to find Milky Way GCs potentially hosting an intermediate-mass black hole.