Tidal interaction in binary black hole inspiral

TL;DR

This paper explores how tidal interactions between rapidly rotating black holes in binary systems can significantly influence gravitational wave signals, energy emission, and angular momentum distribution during inspiral.

Contribution

It highlights the potential importance of tidal torque effects in black hole binaries with aligned, large angular momenta, suggesting a focus for numerical relativity studies.

Findings

Tidal torque may modify the gravitational wave chirp at inspiral endpoint.

Tidal transfer can increase energy radiated during inspiral.

Tidal effects may help shed excess angular momentum.

Abstract

In rotating viscous fluid stars, tidal torque leads to an exchange of spin and orbital angular momentum. The horizon of a black hole has an effective viscosity that is large compared to that of stellar fluids, and an effective tidal torque may lead to important effects in the strong field interaction at the endpoint of the inspiral of two rapidly rotating holes. In the most interesting case both holes are maximally rotating and all angular momenta (orbital and spins) are aligned. We point out here that in such a case (i) the transfer of angular momentum may have an important effect in modifying the gravitational wave ``chirp'' at the endpoint of inspiral. (ii) The tidal transfer of spin energy to orbital energy may increase the amount of energy being radiated. (iii) Tidal transfer in such systems may provide a mechanism for shedding excess angular momentum. We argue that numerical relativity, the only tool for determining the importance of tidal torque, should be more specifically focused on binary configurations with aligned, large, angular momenta.