EAPSI: Search for Milky Way Black Holes in the Southern Globular Clusters

Shishkovsky Laura K, East Lansing MI

Investigators

Abstract

Globular clusters are dense populations of hundreds of thousands to millions of stars, and were expected to at one point also contain a population of around 1000 stellar-mass black holes. However, theory predicted that as the clusters evolved, these black holes would be ejected from the cluster through gravitationsal interactions with other black holes, leaving only ~1-2% of globular clusters with a stellar-mass black holes. Recent research suggests though, that stellar-mass black holes could be far more common in globular clusters. This project aims to investigate the frequency of black holes in globular clusters using radio observations of Milky Way globular clusters from the Australian Telescope Compact Array (ATCA), and has the potential to increase the number of known black holes in the Milky Way significantly. This work will be done under the supervision of host researcher James Miller-Jones of Curtin University, whose expertise in this subject and access to ATCA are critical to the success of the project. This project will focus the search for stellar-­mass black holes on cores of the clusters where, through dynamical mass-segregation, these black holes are expected to be. Radio observations are increasingly sensitive to low-­luminosity accretion onto compact objects, which makes the deep ATCA observations ideal for this search. Stellar-­mass black hole candidates will be identified by their flat spectrum radio emission, and followed up with observations at different wavelengths to confirm that candidates are not accreting neutron stars, white dwarfs, or background galaxies. If stellar-­mass black holes are indeed common in globular clusters, this would have significant implications, such as that more accurate study of stellar-­mass black holes could be done, and there would be increased chance of the formation of black hole-­black hole binaries, which would be important sources of gravitational waves. This NSF EAPSI award is funded in collaboration with the Australian Academy of Science.