http://arxiv.org/abs/1711.07142
The binary black hole mergers detected by Advanced LIGO/Virgo have shown no evidence of large black hole spins. However, because LIGO/Virgo best measures the effective combination of the two spins along the orbital angular momentum (chi_eff), it is difficult to distinguish between binaries with slowly-spinning black holes and binaries with spins lying in the orbital plane. Here, we study the spin dynamics for binaries with a third black hole companion, and identify a new dynamical process which preferentially leads to binary black hole mergers with small chi_eff. While the binary undergoes fast Lidov-Kozai oscillations, the two black hole spins slowly rotate onto the plane perpendicular to the total angular momentum of the triple. For spins initially aligned with the orbital angular momentum of the binary, the differential rotation of the spin vectors onto a fixed plane causes chi_eff to “freeze” near zero as the orbit decays through the emission of gravitational waves. Through a population study, we show that this effect predominantly produces binaries with near-zero chi_eff even for maximally-spinning black holes. We conclude that such triples could provide a natural explanation for the low chi_eff values of the binary black hole mergers without the need to invoke unrealistically small black hole spins.
F. Antonini, C. Rodriguez, C. Petrovich, et. al.
Tue, 21 Nov 17
69/79
Comments: 6 pages, 3 figure. Submitted to PRL