It has been assumed that intermediate-mass black holes (IMBHs) in
globular clusters can only reside in the most centrally concentrated
clusters, with a so-called `core-collapsed' density profile. While
this would be a natural guess, it is in fact wrong. We have followed
the evolution of star clusters containing IMBHs with masses between
$125 \le M_{BH} \le 1000$ $M_{\odot}$ through detailed $N$-body
simulations, and we find that a cluster with an IMBH, in projection,
appears to have a relatively large `core' with surface brightness only
slightly rising toward the center. This makes it highly unlikely that
any of `core-collapsed' clusters will harbor an IMBH. On the contrary,
the places to look for an IMBH are those clusters that can be fitted
well by medium-concentration King models.
The velocity dispersion of the visible stars in a globular cluster
with an IMBH is nearly constant well inside the apparent core
radius. For a cluster of mass $M_C$ containing an IMBH of mass
$M_{BH}$, the influence of the IMBH becomes significant only at a
fraction $2.5 M_{BH}/M_C$ of the half-mass radius, deep within the
core, where it will affect only a small number of stars. In
conclusion, observational detection of an IMBH may be possible, but
will be challenging.
Complete paper: pdf file (197 KBytes)