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

In this paper, we discuss how the structural and observational properties of globular clusters (GCs) can be used to infer the presence of a black hole system (BHS) inhabiting their inner regions. We propose a novel way to define the BHS size as the radius from the GC centre within which half of the mass is in stellar mass BHs and the remaining half is in other stars. 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, pc(-3) and composed of relatively massive BHs, with average masses in the range mBHS = 14 - 22M(circle dot). We also show that a similar approach can be used to find Milky Way GCs potentially hosting an intermediate-mass black hole.