Thursday, July 25, 2013

1307.6237 (Carlos O. Lousto et al.)

Where angular momentum goes in a precessing black hole binary    [PDF]

Carlos O. Lousto, Yosef Zlochower
We evolve a set of 32 equal-mass black-hole binaries with collinear spins (with intrinsic spin magnitudes 0.8 of the maximum allowed) to study the effects of precession in the highly nonlinear plunge and merger regimes. We compare the direction of the instantaneous radiated angular momentum, to the directions of the total angular momentum and the orbital angular momentum$. We find that the radiated angular momentum approximately follows the orbital angular momentum throughout the evolution. During the orbital evolution and merger, we observe that the angle between the orbital angular momentum and total spin is approximately conserved, which allows us to propose and test models for the merger remnant black hole's mass and spin. For instance, we verify that the hangup effect is the dominant effect and largely explains the observed total energy and angular momentum radiated by these precessing systems. We also find that the total angular momentum, while significantly decreasing in magnitude during the simulations, varies from its initial direction by < 5 deg. The maximum variation in the direction of the total angular momentum occurs when the spins are nearly antialigned with the orbital angular momentum. Based on our results, we conjecture that transitional precession, which would lead to large variations in the direction of the total angular momentum, is not possible for similar-mass binaries.
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