Searching for intermediate-mass black holes in globular clusters with gravitational microlensing

N. Kains, D. M. Bramich, K. C. Sahu, A. Calamida

Research output: Contribution to journalArticle

9 Citations (Scopus)


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 intermediate-mass black hole (IMBH) detection via astrometric microlensing. If M 22 hosts an IMBH of mass 105 M, then the probability that at least one star will yield a detectable signal over an observational baseline of 20 years is ~86 per cent, while the probability of a null result is around 14 per cent. For an IMBH of mass 106 M, the detection probability rises to >99 per cent. Future observing facilities will also extend the available time baseline, improving the chance of detections for the clusters we consider.

Original languageEnglish
Pages (from-to)2025-2035
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - 2016
Externally publishedYes



  • Globular clusters: general
  • Gravitational lensing: micro
  • Stars: black holes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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