Searching for intermediate-mass black holes in globular clusters with
  gravitational microlensing
  We discuss the potential of the gravitational microlensing method as a unique
tool to detect unambiguous signals caused by intermediate-mass black holes in
globular clusters. We select clusters near the line of sight to the Galactic
Bulge and the Small Magellanic Cloud, estimate the density of background stars
for each of them, and carry out simulations in order to estimate the
probabilities of detecting the astrometric signatures caused by black hole
lensing. We find that for several clusters, the probability of detecting such
an event is significant with available archival data from the Hubble Space
Telescope. Specifically, we find that M 22 is the cluster with the best chances
of yielding an IMBH detection via astrometric microlensing. If M 22 hosts an
IMBH of mass $10^5M_\odot$, then the probability that at least one star will
yield a detectable signal over an observational baseline of 20 years is $\sim
86\%$, while the probability of a null result is around $14\%$. For an IMBH of
mass $10^6M_\odot$, the detection probability rises to $>99\%$. Future
observing facilities will also extend the available time baseline, improving
the chance of detections for the clusters we consider.
