Binary black hole merger gravitational waves and recoil in the large mass ratio limit

TL;DR

This paper introduces a perturbation theory-based code to model gravitational waves from binary black hole mergers with large mass ratios, focusing on recoil effects and the antikick phenomenon.

Contribution

It presents the first results of a new computational approach for large mass ratio binaries, extending the modeling capabilities beyond current numerical relativity limitations.

Findings

Recoil grows with black hole spin for aligned orbits.

Total recoil is minimized for prograde and maximized for retrograde coalescence.

Reversal of kick versus spin trend compared to inspiral-only analyses.

Abstract

Spectacular breakthroughs in numerical relativity now make it possible to compute spacetime dynamics in almost complete generality, allowing us to model the coalescence and merger of binary black holes with essentially no approximations. The primary limitation of these calculations is now computational. In particular, it is difficult to model systems with large mass ratio and large spins, since one must accurately resolve the multiple lengthscales which play a role in such systems. Perturbation theory can play an important role in extending the reach of computational modeling for binary systems. In this paper, we present first results of a code which allows us to model the gravitational waves generated by the inspiral, merger, and ringdown of a binary system in which one member of the binary is much more massive than the other. This allows us to accurately calibrate binary dynamics in the large mass ratio regime. We focus in this analysis on the recoil imparted to the merged remnant by these waves. We closely examine the "antikick", an anti-phase cancellation of the recoil arising from the plunge and ringdown waves, described in detail by Schnittman et al. We find that, for orbits aligned with the black hole spin, the antikick grows as a function of spin. The total recoil is smallest for prograde coalescence into a rapidly rotating black hole, and largest for retrograde coalescence. Amusingly, this completely reverses the predicted trend for kick versus spin from analyses that only include inspiral information.