  Establishing or ruling out, either through solid mass measurements or upper
limits, the presence of intermediate-mass black holes (IMBHs) at the centers of
star clusters would profoundly impact our understanding of problems ranging
from the formation and long-term dynamical evolution of stellar systems, to the
nature of the seeds and the growth mechanisms of supermassive black holes.
While there are sound theoretical arguments both for and against their presence
in today's clusters, observational studies have so far not yielded truly
conclusive IMBH detections nor upper limits. We argue that the most promising
approach to solving this issue is provided by the combination of measurements
of the proper motions of stars at the centers of Galactic globular clusters and
dynamical models able to take full advantage of this type of data set. We
present a program based on HST observations and recently developed tools for
dynamical analysis designed to do just that.
