The fingerprint of binary intermediate-mass black holes in globular clusters: Suprathermal stars and angular momentum alignment

We explore the signatures that a binary intermediate-mass black hole (IMBH) imprints on the velocity and on the angular momentum of globular cluster (GC) stars. Simulating three-body encounters between a star and a binary IMBH, we find that the binary IMBH generates a family of a few hundred stars (∼ 100-300) which remain bound to the GC and have velocity significantly higher than the dispersion velocity. For this reason, we term them 'suprathermal' stars. We also notice that, after the interaction, a considerable fraction (55-70 per cent) of stars tend to align their orbital angular momentum with the angular momentum of the binary IMBH, introducing an anisotropy in the angular momentum distribution of cluster stars. We simulate the dynamical evolution of these suprathermal stars before thermalization and find that these stars tend to cluster at a distance of few core radii from the GC centre. We conclude that the detectability of such signatures appears problematic with present telescopes.