  As self-gravitating systems, dense star clusters exhibit a natural diffusion
of energy from their innermost to outermost regions, which leads to a slow and
steady contraction of the core until it ultimately collapses under gravity.
However, in spite of the natural tendency toward so-called "core collapse," the
globular clusters (GCs) in the Milky Way exhibit a well-observed bimodal
distribution in core radii separating the core-collapsed and non-core-collapsed
clusters. This suggests an internal energy source is at work, delaying the
onset of core collapse in many clusters. Primordial binary stars have been
thought for a long time to provide this energy source, but recent analyses have
cast doubt upon the corresponding "binary-burning" mechanism as a viable
explanation. Over the past decade, a large amount of both observational and
theoretical work has suggested that many stellar-mass black holes (BHs) are
retained in typical clusters today and that they play a dynamically-significant
role in these clusters throughout their entire lifetimes. Here we review our
latest understanding of the formation and evolution of BH populations in GCs
and demonstrate that, through their dynamical interaction with their host
cluster, BHs can naturally explain the distinction between core-collapsed and
non-core-collapsed clusters through a process we call "black hole burning."

Astrophysics of Galaxies;High Energy Astrophysical Phenomena