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Authors: Michael Koppitz, Denis Pollney, Christian Reisswig, Luciano Rezzolla, Jonathan Thornburg, Peter Diener, Erik Schnetter

Date: Mon, 29 Jan 2007

Abstract: The final evolution of a generic binary black-hole system is expected to give rise to a net recoil velocity as a result of the asymmetry in the beamed gravitational radiation emitted. A quantitative measurement of this effect in the case of binaries with unequal masses has been recently computed by a number of different groups in full numerical-relativity simulations. These have pointed out that kick velocities as large as 175 km/s can be reached for a mass ratio $q\equiv M_1/M_2\simeq 0.36$, where $M_1$ and $M_2$ are the masses of the two black holes. However, a recoil velocity can also be obtained for equal-mass binaries with spinning black holes that have unequal spins. We report here on numerical evolutions of such binary black-hole systems and show, using two independent methods, that even larger kick velocities are possible, with a maximum of $257 \pm 15$ km/s for a system having a spin ratio $a_1/a_2 = -1$ and $a_2\equiv S_2/mˆ2_2=0.584$. This extrapolates to $\sim 450$ km/s for extremal black holes. Such large velocities are not unexpected and we show that the numerical results reproduce, at least qualitatively, the post-Newtonian predictions.

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