Investigating high-velocity stars ejected from the cores of globular clusters

Abstract

The dense environment in the cores of globular clusters enables three-body interactions involving a binary system and a single star to occur frequently, which can eject high-velocity stars from the cluster. The velocities of these stars reflect the masses involved in the interactions which accelerated them, making them promising tracers of stellar remnants in globular clusters, particularly the black hole population. We use <i>Gaia</i> Data Release 3 data to locate high-velocity stars in the regions around a large number of Milky Way globular clusters, finding over 2000 candidates for 53 of the investigated clusters. Thirteen of these clusters are selected for further analysis in order to determine the potential origins of the observed high-velocity stars. The velocity distribution of the ejected high-velocity stars is predicted analytically and compared to the observed samples for a number of scenarios of different three-body interactions, mostly involving compact objects such as black holes. We can determine that the likely object which has been involved in the interaction that produced these stars must be a black hole for some cases. We have found evidence of the presence of black holes in nine globular clusters. We discuss future directions and improvements to this work which will allow for further constraints on black hole populations within globular clusters