Dancing with the Black Holes: Spin Secrets of Merging Binaries

Gravitational waves have uncovered a treasure trove of nearly 90 merging black holes and neutron stars, each with its own unique story to tell. In this talk, our focus centers on black hole spins, seeking to decipher the secrets hidden within, including their origins, hometowns, and the forces driving their mergers. We'll begin by peering into the heart of star clusters, where dynamical processes give rise to second-generation (2g) black holes and explore how their spins set them apart. These spins become a powerful tool for identifying them, and we discuss their significance in recent gravitational wave detections like GW190521 and GW190412. Shifting focus, we will challenge the conventional belief that isolated binary black holes should have spins aligned with orbital angular momentum. We will explore mechanisms that can influence spins before and during supernovae, leaving distinct imprints in observable spin distributions.