How can we measure spin precession for heavy binary black holes using gravitational waves?

The spins of black holes (BHs) in binary black hole (BBH) systems offer a unique probe of physics on multiple scales, from stellar interiors to the astrophysical environments in which compact binaries form. Despite their astrophysical importance, spin magnitudes and tilt angles for BBHs remain poorly constrained using gravitational-wave (GW) data from the Laser Interferometer GW Observatory (LIGO). The components of spin lying in the orbital plane, causing precession, are particularly hard to measure due to their weak imprint on GW signals and ability to mimic other physical effects. As a spurious measurement of precession could arise from a non-astrophysical source (i.e. small fluctuations in detector noise, data quality issues, waveform systematics, etc.), it is imperative that any claims of detected precession are supported via a robust understanding of where in waveforms and for what types of systems precession is measurable. Using results from time-domain parameter estimation with state-of-the-art numerical relativity surrogate waveforms, I will discuss the roles of the inspiral or merger phases of coalescence in measuring precession for high-mass BBHs. I present LIGO's BBH event GW190521 as a case study, and explore simulated signals of related systems.