AR 12845 (Archival Research)

Fri Dec 8 08:39:12 GMT 2023

Principal Investigator: Andrea Bellini
PI Institution: Space Telescope Science Institute
Investigators (xml)

Title: Hunting for Intermediate-Mass Black Holes: Archival Proper-Motion Analysis of Globular Clusters
Cycle: 20

The unambiguous detection of an intermediate mass black hole {IMBH} in a globular star cluster would be a major achievement for the Hubble Space Telescope. It is critical to know whether or not IMBHs exist in the centers of clusters in order to understand the dynamical evolution of dense stellar systems. Also, an IMBH detection would prove the existence of BHs in an entirely new mass range. Observationally, the search has been hampered by the low number of stars with known velocities in the central few arcseconds. This limits measurements of the stellar velocity dispersion in the region where the gravitational influence of any IMBH would be felt. Existing IMBH claims in the literature have all been called into question, and have all been based on line-of-sight velocities from spectroscopy. We propose to derive a homogeneus set of high-precision proper motions in the cores of 12 globular clusters for which there exist suitable multi-epoch ACS and WFC3 datasets in the archive, and either detect or place firm constraints on the presence of an IMBH in them. Seven of these clusters are known to harbor multiple populations of stars. For them, in addition, we will also be able to derive luminosity and mass functions for the different subpopulations and measure possible differences in their velocity distributions, as merging-formation theories suggest. Many other projects will benefit from our high-precision proper-motion measurements {bona-fide membership determination, detailed cluster modeling, etc.}, so we will make our catalogs available to the astronomical community.