Detection of IMBHs from microlensing in globular clusters

Margarita Safonova, Sohrab Rahvar
  • Proceedings of the International Astronomical Union, August 2006, Cambridge University Press
  • DOI: 10.1017/s1743921307005844

IMBH in globular clusters

What is it about?

The intermediate-mass black holes (IMBHs), with masses in the range 100 − 1000 M⊙ , are a logical bridge between the stellar-mass black holes (BHs) and supermassive BHs. However, in spite of considerable theoretical backing for their formation and existence, firm observational evidence has remained elusive. Extrapolating the well-established M• -σ correlation for galaxies down the BH mass ladder suggests that IMBHs can reside in smaller stellar systems such as dwarf galaxies and globular clusters (GCs). A few normal dwarfs and globular clusters have been reported to host the IMBHs. However, none of the existing/proposed methods present an unambiguous signature of a massive central BH in GCs. Gravitational Microlensing (ML), on the other hand, is a method that is ideally suited to directly resolve both the presence and the nature of the central IMBH in GCs. We propose monitoring GCs for the ML search of IMBHs. These observations will be subjected to Differential Imaging Analysis (DIA) to extract the ML signal, with can easily be discriminated from the much shorter stellar variables and self-lensing events. Given that IMBHs are an important issue in the modern astronomy we hope that with our observations, the unambiguous detection (or otherwise) will be possible.

Why is it important?

IMBHs are an important issue in the modern astronomy. Determining whether IMBHs are common in GCs is a key problem in astrophysics, because of the important consequences for their structure, kinematics, internal energies, and long-term dynamical evolution. In addition, IMBHs are crucial to link formation processes of stellar-mass BHs and SMBHs, and could serve as seeds for the growth of SMBHs. Extending the local BH mass function to the extreme low end of the mass ladder is key to understanding whether there is a minimum galaxy mass or velocity dispersion below which BHs are unable to grow.

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The following have contributed to this page: Dr Margarita Safonova