James Miller-Jones (Curtin)

James Miller-Jones colloquium: Quiescent black holes in globular clusters

Marsfield Lecture Theatre

Abstract

Title: Quiescent black holes in globular clusters: the nature of low-luminosity accretion

Abstract:

Although several hundred stellar-mass black holes are believed to form early in the lifetime of a globular cluster from the deaths of the most massive stars, it was thought that they would then mass segregate to the cluster centre, causing most of them to be ejected via mutual gravitational interactions. Using deep radio continuum observations, we have recently found the first strong evidence for stellar-mass black holes in Galactic globular clusters, challenging this theoretical expectation. I will present our initial results, and outline ongoing follow-up campaigns to verify the black hole nature of these sources, as well as a major radio survey to determine the demographics of this newly-discovered population of candidate black holes. In the second half of the talk, I will describe the potential implications of this work. The low luminosities of these weakly-accreting sources make them ideal probes of the poorly-understood quiescent state in which the overwhelming majority of stellar-mass black holes exist. The known distances to globular clusters can provide more accurate estimates of the physical parameters of these black holes than exist for typical field sources, and the additional formation channels available in a dense cluster should provide a less biased estimate of the black hole mass function than the known field sources.