Parameter estimation of binary black holes in the endpoint of the up-down instability

Understand

Black-hole binary spin precession admits equilibrium solutions corresponding to systems with (anti-) aligned spins.

• Among these, binaries in the up-down configuration, where the spin of the heavier (lighter) black hole is co- (counter-) aligned with the orbital angular momentum, might be unstable to small perturbations of the spin directions.
• The occurrence of the up-down instability leads to gravitational-wave sources that formed with aligned spins but are detected with precessing spins.
• We present a Bayesian procedure based on the Savage-Dickey density ratio to test the up-down origin of gravitational-wave events.