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

We performed a series of 1341 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

$26,677pm 470$ km/s, thus nearly $9\%$ the speed of light.