Ultimate Black Hole Recoil: What is the Maximum High-Energy Collision Kick?

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 +/- 342 km/s, thus approximately bounded by 10% of the speed of light.