Abstract

How do black holes spin? Unlike in Newtonian gravity, if two black holes are gravitationally bound, then their spins will interact with each other, and notably the orbital angular momentum. This causes the orbital plane to tilt, leading to a modulation of the phase and amplitude of the gravitational waves emitted by the binary. These modulations are complex combinations of the individual spin parameters, motivating gravitational wave measurements to be reported using two effective parameters, $\chi_{\rm eff}$ and $\chi_{P}$. These parameters are useful from a waveform perspective, but can obscure the rich spin dynamics of the two black holes during the inspiral. In this talk, I will present an alternative approach to spin precession classification, through the introduction of five phenomenological parameters. These parameters disentangle the motion of the orbital angular momentum into its azimuthal motion (precession), and its polar motion (nutation). This complimentary method allows us to capture some of the key features of the spin precession taxonomy, thus more closely following the spin dynamics of the black hole binary. I will also show a follow up study where we constrain the five parameters in the gravitational wave catalogs using the LIGO -Virgo-KAGRA (LVK) parameter estimation samples. In agreement with current population constraints, the results find evidence of precession in the gravitational wave events. While constraints on the orbital angular momentum nutation of individual events in the catalogs are weak, with future LVK sensitivities the detection of nutation becomes a possibility.