Modeling kicks from the merger of generic black-hole binaries

TL;DR

This paper investigates the recoil velocities from merging black-hole binaries, revealing that the maximum kicks scale with the cube of the symmetric mass ratio, which impacts astrophysical models of black hole retention.

Contribution

It provides new numerical simulations showing the recoil velocity scaling with the symmetric mass ratio as approximately η^3, refining previous models.

Findings

Maximum recoil kick perpendicular to the orbital plane scales as η^3.

Scaling differs from the previously proposed η^2 dependence.

Implications for black hole retention in galaxies and clusters.

Abstract

Recent numerical relativistic results demonstrate that the merger of comparable-mass spinning black holes has a maximum ``recoil kick'' of up to $\sim 4000 \kms$. However the scaling of these recoil velocities with mass ratio is poorly understood. We present new runs showing that the maximum possible kick perpendicular to the orbital plane does not scale as $\sim\eta^2$ (where $\eta$ is the symmetric mass ratio), as previously proposed, but is more consistent with $\sim\eta^3$, at least for systems with low orbital precession. We discuss the effect of this dependence on galactic ejection scenarios and retention of intermediate-mass black holes in globular clusters.