Population measurements of the binary black hole effective spin after LIGO/Virgo's O3 observing run

Upon the conclusion of the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo's third observing run (O3), we now have over 70 cataloged binary black hole (BBH) mergers. From these detections, we can continue to measure the distribution of spin across the BBH population, a property which is essential to understanding the astrophysical origins of these systems and how they evolve over time. I will discuss what we can infer in particular about the so-called effective and precessing spins of the known BBH population following O3. Using Bayesian hierarchical inference, I fit several different parameterized models to the population, beginning with simplistic unimodal distributions and then expanding to fit for possible extra underlying features.