Influence of tidal dissipation on outcomes of binary-single encounters between stars and black holes in stellar clusters

TL;DR

This study investigates how tidal dissipation affects the outcomes of binary-single encounters involving black holes and stars in stellar clusters, revealing significant increases in BH-star mergers when tides are considered.

Contribution

It introduces the systematic inclusion of dynamical tides in simulations of binary-single encounters, showing their impact on merger rates in stellar cluster environments.

Findings

Tides increase BH-star mergers by up to 75%.

Including PN corrections raises BH-BH merger counts.

Tides do not significantly affect BH-BH mergers.

Abstract

In the cores of dense stellar clusters, close gravitational encounters between binary and single stars can frequently occur. Using the Tsunami code, we computed the outcome of a large number of binary-single interactions involving two black holes (BHs) and a star to check how the inclusion of orbital energy losses due to tidal dissipation can change the outcome of these chaotic interactions. Each interaction was first simulated without any dissipative processes and then we systematically added orbital energy losses due to gravitational wave emission (using post-Newtonian (PN) corrections) and dynamical tides and recomputed the interactions. We find that the inclusion of tides increases the number of BH-star mergers by up to 75 per cent but it does not affect the number of BH-BH mergers. These results highlight the importance of including orbital energy dissipation due to dynamical tides during few-body encounters and evolution of close binary systems within stellar cluster simulations. Consistent with previous studies, we find that the inclusion of PN terms increases the number of BH-BH mergers during binary-single encounters. However, BH-star mergers are largely unaffected by the inclusion of these terms.