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Abstract: The inspiral of binary black holes is governed by gravitational radiationreaction at binary separations r < 1000 M, yet it is too computationallyexpensive to begin numerical-relativity simulations with initial separations r> 10 M. Fortunately, binary evolution between these separations is welldescribed by post-Newtonian equations of motion. We examine how thispost-Newtonian evolution affects the distribution of spin orientations atseparations r ~ 10 M where numerical-relativity simulations typically begin.Although isotropic spin distributions at r ~ 1000 M remain isotropic at r ~ 10M, distributions that are initially partially aligned with the orbital angularmomentum can be significantly distorted during the post-Newtonian inspiral.Spin precession tends to align anti-align the binary black hole spins witheach other if the spin of the more massive black hole is initially partiallyaligned anti-aligned with the orbital angular momentum, thus increasingdecreasing the average final spin. Spin precession is stronger forcomparable-mass binaries, and could produce significant spin alignment beforemerger for both supermassive and stellar-mass black hole binaries. We alsopoint out that precession induces an intrinsic accuracy limitation < 0.03 inthe dimensionless spin magnitude, < 20 degrees in the direction in predictingthe final spin resulting from the merger of widely separated binaries.



Author: Michael Kesden, Ulrich Sperhake, Emanuele Berti

Source: https://arxiv.org/







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