What is it about?

Every galaxy we seem to look at has a supermassive black hole in the center. They are the black holes with masses in the range million to a billion solar masses, called so to distinguish them from the stellar mass black holes produced by the death of massive stars. There is no dearth of stellar-mass (1–15 solar masses) black holes either; by some estimates there may be ten to 10 to 100 million of them in every galaxy. But black holes in the middle range are still elusive.

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Why is it important?

IMBH have long been proposed to reside in the centers of globular clusters. But resolving the centers of globular clusters is very difficult as these are very dense stellar systems. We propose to consider the microlensing events that are expected when globular cluster stars pass behind the central IMBH that acts as a lens, inducing amplification of light. In this case we need not resolve individual stars, just observe the change in the central brightness.

Perspectives

Determining whether globular clusters contain IMBHs is a key problem in astronomy. Their cosmic mass density could exceed that of supermassive black holes and the observations do not even rule out that they may account for all the baryonic dark matter in the Universe. They also may have profound influence on the evolution and survival of globular clusters, as well as on the growth of the supermassive black holes. By observing large enough number of globular clusters there is a chance to prove the existence of an IMBH.

Dr Margarita Safonova
Indian Institute of Astrophysics

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This page is a summary of: Detection of IMBHs from Microlensing in Globular Clusters, January 2008, American Institute of Physics,
DOI: 10.1063/1.3009470.
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