Up Down

Binary black holes with exactly aligned spins remain aligned for all time. My collaborators and I have just discovered an instability: if more massive black hole has spin up (parallel to L) and the less massive black hole has spin down (antiparallel to L), then certain binaries will inevitably become unstable to spin precession, rapidly evolving to large misalignment. This instability could occur in observationally accessible astrophysical compact binaries, including supermassive binary black holes, with significant impact on the light and gravitational waves such an object would emit.

For experts Both analytically and via direct integration of the orbit-averaged 2PN spin precession equations, we have demonstrated that the up/down spin configuration is unstable; that the instability’s nonlinear evolution can be understood analytically, via our previously-described nonlinear spin precession solution; that it occurs for a wide range of masses, spins, and mass ratios; and that, if nature creates up/down binaries, evidence of the instability will be present in the sensitive band of existing and future gravitational wave detectors like LIGO, LISA, and pulsar timing arrays.

For more information, see

• Gerosa et al 2015 Precessional instability in binary black holes with aligned spins, a PRL editor’s suggestion

• Animations of the three figures in our paper (one, two, three); see Davide Gerosa’s page.