Recoil Velocities from Equal-Mass Binary-Black-Hole Mergers

TL;DR

This paper investigates the recoil velocities resulting from equal-mass binary black hole mergers, demonstrating that significant kicks up to 440 km/s can occur when spins are asymmetrically aligned or antialigned.

Contribution

It provides new estimates of recoil velocities for equal-mass black hole mergers with specific spin configurations, using two independent methods.

Findings

Recoil velocities up to 440 km/s for certain spin configurations.

Equal-mass binaries can produce larger kicks than previously thought.

Two independent methods confirm the high recoil velocities.

Abstract

The final evolution of a binary black-hole system gives rise to a recoil velocity if an asymmetry is present in the emitted gravitational radiation. Measurements of this effect for non-spinning binaries with unequal masses have pointed out that kick velocities $\sim~175$ km/s can be reached for a mass ratio $\simeq 0.36$. However, a larger recoil can be obtained for equal-mass binaries if the asymmetry is provided by the spins. Using two independent methods we show that the merger of such binaries yields velocities as large as $\sim 440$ km/s for black holes having unequal spins that are antialigned and parallel to the orbital angular momentum.