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Alice Zocchi

Dr Alice Zocchi

Dr Alice Zocchi

Research Fellow

Interests and expertise (Subject groups)

Grants awarded

Unique signatures of intermediate-mass black holes in globular clusters

Scheme: Newton International Fellowships

Organisation: University of Surrey

Dates: May 2014-Feb 2016

Value: £88,500

Summary: Black holes with masses in excess of a million solar masses are found in the centres of almost all galaxies, including our own Milky Way. The discovery of these super-massive black holes (SMBHs) at high redshift is a challenge for models of galaxy formation. The required growth is extremely high if the seed is an ordinary stellar BH with a mass of a few tens of solar masses. It has then been suggested that intermediate-mass black holes (IMBHs) could be the seeds for SMBHs, but convincing observational evidence for the existence of IMBHs is still lacking. Two popular theories for the formation of an IMBH exist: they could be the end product of Population III stars, or they could be the result of runaway stellar collisions in dense young globular clusters (GCs). The extrapolation of the empirical relation between SMBHs masses and the velocity dispersion of their host also suggests that IMBHs are expected in GCs. For our understanding of the formation and evolution of both GCs and their host galaxy, it is of key importance to establish whether the elusive IMBHs in fact reside in the cores of GCs, or not. This is challenging because the predicted signatures of an IMBH are degenerate with alternative, more plausible, scenarios. Indeed, observational claims of IMBH detections in GCs are mostly based on the discovery of a shallow cusp in the surface brightness profile and a rise in the velocity dispersion profile towards the centre: the first evidence could be due to mass segregation, core collapse, or the presence of binary stars in the centre, while the second could be caused by the presence of radially-biased pressure anisotropy. The goal of this project is to identify a unique observational signature (the "smoking gun") of IMBHs in the kinematics of stars in GCs.

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