A General Formula for Black Hole Gravitational Wave Kicks

TL;DR

This paper presents a unified formula for the out-of-plane gravitational wave kicks of merging black holes, resolving previous conflicting models and fitting existing data with high accuracy, which is crucial for understanding black hole ejections from galaxies.

Contribution

It introduces a new ansatz for the out-of-plane kick that unifies previous models and fits all existing data within 5% accuracy.

Findings

Unified formula fits almost all data within 5%

Previous conflicts due to different data sets and parameter space exploration

Out-of-plane kicks can reach over 500 km/s, affecting galaxy dynamics

Abstract

Although the gravitational wave kick velocity in the orbital plane of coalescing black holes has been understood for some time, apparently conflicting formulae have been proposed for the dominant out-of-plane kick, each a good fit to different data sets. This is important to resolve because it is only the out-of-plane kicks that can reach more than 500 km/s and can thus eject merged remnants from galaxies. Using a different ansatz for the out-of-plane kick, we show that we can fit almost all existing data to better than 5 %. This is good enough for any astrophysical calculation, and shows that the previous apparent conflict was only because the two data sets explored different aspects of the kick parameter space.