Ultimate Black Hole Recoil: What the maximum high energy collisions kick is?

Abstract

We performed a series of 1381 full numerical simulations of high energy collision of black holes to search for the maximum recoil velocity after their merger. We consider equal mass binaries with opposite spins pointing along their orbital plane and perform a search of spin orientations, impact parameters, and initial linear momenta to find the maximum recoil for a given spin magnitude $s$. This spin sequence for $s=0.4, 0.7, 0.8, 0.85, 0.9$ is then extrapolated to the extreme case, $s=1$, to obtain an estimated maximum recoil velocity of $28,562\pm 342$ km/s, thus approximately bounded by $10\%$ the speed of light.