dc.description.abstract | Binary black holes on quasicircular orbits with spins aligned with their orbital angular momentum
have been testbeds 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$_{ud±}$ = ($\sqrt{χ1}$ ± $\sqrt{qχ2}$)$^{4}$(1 - q)$^{-2}$ M, where M is the total mass, q ≡ m$_{2}$=m$_{1}$ 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 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. | |