# Kicking gravitational wave detectors with recoiling black holes

## TL;DR

This paper presents new numerical simulations of black hole mergers with high recoil velocities, introduces a novel method to analyze recoil dependence on merger phase, and assesses the detectability of these events with gravitational wave detectors.

## Contribution

It provides eight new simulations of maximally spinning black hole mergers, introduces an invariant waveform analysis method, and evaluates the observability of high recoil events.

## Key findings

- Maximum recoil velocities up to ~4700 km/s were achieved.
- The waveform peak amplitude serves as an effective phase reference.
- Highly recoiling black holes can be distinguished by gravitational wave detectors.

## Abstract

Binary black holes emit gravitational radiation with net linear momentum leading to a retreat of the final remnant black hole that can reach up to $\sim5,000$ km/s. Full numerical relativity simulations are the only tool to accurately compute these recoils since they are largely produced when the black hole horizons are about to merge and they are strongly dependent on their spin orientations at that moment. We present eight new numerical simulations of BBH in the hangup-kick configuration family, leading to the maximum recoil. Black holes are equal mass and near maximally spinning ($|\vec{S}_{1,2}|/m_{1,2}^2=0.97$). Depending on their phase at merger, this family leads to $\sim\pm4,700$ km/s and all intermediate values of the recoil along the orbital angular momentum of the binary system. We introduce a new invariant method to evaluate the recoil dependence on the merger phase via the waveform peak amplitude used as a reference phase angle and compare it with previous definitions. We also compute the mismatch between these hangup-kick waveforms to infer their observable differentiability by gravitational wave detectors, such as advanced LIGO, finding currently reachable signal-to-noise ratios, hence allowing for the identification of highly recoiling black holes having otherwise essentially the same binary parameters.