On black hole sub-systems in idealized nuclear star clusters
  Recent observational evidence, numerical simulations and theoretical
arguments seem to indicate that stellar mass black holes (BH) persist in
stellar systems such as globular star clusters for much longer than previously
thought. Previously, theory implied that the BH would segregate into a compact
system with short dynamical time scales, and that the BH would escape long
before the present. But stellar systems can exist in a state of balanced
evolution, where the energy generated in the core is regulated by the process
of two-body relaxation in the bulk of the system. If the system has a centrally
concentrated BH subsystem and there is no massive central BH, then the energy
is generated by three-body encounters in the core of this subsystem. Therefore,
in balanced evolution, the evolution of the BH subsystem is regulated by the
much longer time scales of the host system. In the present paper the
implications of these results for idealized nuclear star clusters (NSC) are
discussed. Though previous theory implied that BH would be almost absent from
many NSC -- those with relatively short dynamical time scales -- it is argued
here that, based on the results of idealized models, many such NSC could still
be host to substantial BH subsystems.
