Precessional Instability in Binary Black Holes with Aligned Spins


Binary black holes on quasicircular orbits with spins aligned with their orbital angular momentum have been test beds for analytic and numerical relativity for decades, not least because symmetry ensures that such configurations are equilibrium solutions to the spin-precession equations. In this work, we show that these solutions can be unstable when the spin of the higher-mass black hole is aligned with the orbital angular momentum and the spin of the lower-mass black hole is antialigned. Spins in these configurations are unstable to precession to large misalignment when the binary separation r is between the values (r{ud±}= √X̅₁ ± √q̅x̅)⁴ (1-q)⁻² M where M is the total mass, q ≡ m₂/m₁ is the mass ratio, and χ₁ (χ₂) is the dimensionless spin of the more (less) massive black hole. This instability exists for a wide range of spin magnitudes and mass ratios and can occur in the strong-field regime near the merger. We describe the origin and nature of the instability using recently developed analytical techniques to characterize fully generic spin precession. This instability provides a channel to circumvent astrophysical spin alignment at large binary separations, allowing significant spin precession prior to merger affecting both gravitational-wave and electromagnetic signatures of stellar-mass and supermassive binary black holes.



Angular momentum, Precession, Black holes (Astronomy), Stars--Masses, Resonance

M. K. is supported by Alfred P. Sloan Foundation Grant No. FG-2015-65299. R. O’S. is supported by NSF Grants No. PHY-0970074 and No. PHY-1307429. A. K. and E. B. are supported by NSF CAREER Grant No. PHY-1055103. E. B. acknowledges support from FCT Contract No. IF/00797/2014/CP1214/ CT0012 under the IF2014 Programme. U.S. is supported by FP7-PEOPLE-2011-CIG Grant No. 293412, FP7- PEOPLE-2011-IRSES Grant No. 295189, H2020-MSCARISE- 2015 Grant No. StronGrHEP-690904, SDSC and TACC through XSEDE Grant No. PHY-090003 by the NSF, H2020 ERC Consolidator Grant Agreement No. MaGRaTh-646597, STFC Roller Grant No. ST/ L000636/1 and DiRAC’s Cosmos Shared Memory system through BIS Grant No. ST/J005673/1 and STFC Grant No. ST/H008586/1, ST/K00333X/1. D. T. is partially supported by the NSF Awards No. PHY-1067985 and No. PHY-1404139.


©2015 American Physical Society