Robustly Measuring the Spins of Binary Black Holes with Gravitational Waves

Author: Miller, Simona Jane

Year: 2026

Degree: Dissertation (Ph.D.)

Advisor: Chatziioannou, Katerina

Committee Members: Weinstein, Alan Jay; Chatziioannou, Katerina; Teukolsky, Saul A.; McCuller, Lee P.

Option: Physics

Abstract

Over the past decade, the gravitational-wave (GW) detector network of Advanced LIGO, Advanced Virgo, and KAGRA (LVK) has advanced from the first groundbreaking observation of a merging binary black hole (BBH) to the production of a catalog of hundreds of GW signals from the astrophysical population of compact binaries. I focus on the measurement of one fundamental property of black holes: their spin, or intrinsic angular momentum. Spin is a unique probe of astrophysical processes across scales, from fluid dynamics inside stellar cores to the large-scale evolutionary history of our universe, and is the most promising means of disentangling which of the many proposed BBH formation and evolutionary mechanisms dominate the observed population. GWs remain the only way to directly measure black hole spin, yet spin remains poorly constrained: it has a comparatively weak imprint on GW signals, can mimic other physical effects like eccentricity, and is highly susceptible to features in detector noise and systematic uncertainty in waveform models. Without careful safeguards, we risk spurious spin inference and false astrophysical conclusions. To this end, I develop a suite of computational and statistical methods to produce accurate, precise, and unbiased black hole spin inference at every stage of the LVK's data analysis pipeline. To make spin measurements robust in individual BBH detections, I find that we must connect measured parameters with their phenomenology in GW signals. Then, for the astrophysical BBH population, we need to thoroughly test model behavior against simulated populations, understand the role of Monte Carlo uncertainty, and use data-level parameters to probe model misspecification