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