TAPIR Seminar

In person: 370 Cahill. To Join via Zoom: 868 5298 8404

ABSTRACT: The recent detections of gravitational waves (GW) from merging binary black holes (BBHs) by LIGO/Virgo provide a unique opportunity to investigate black hole properties and the mechanisms behind BBH formation. Despite significant theoretical work, the origins of the GW sources remain an open question. Current theoretical models predicting the rates and characteristics of BBH mergers heavily rely on assumptions regarding stellar mass loss, mass transfer stability, supernova kicks, and accretion physics—many of which remain poorly tested. Additionally, the complex dynamical interactions between stars and black holes in dense stellar environments further complicate their evolutionary pathways. In this talk, I will discuss how these intricate dynamics within dense star clusters impact black hole evolution, leaving distinct imprints on their gravitational-wave signatures. I will particularly highlight how close encounters between black holes and massive stars in young clusters lead to significant spin-up of black holes through accretion. Furthermore, I will address the anisotropic spin distributions observed in recent black hole merger catalogs, which challenge the assumption of isotropy typically expected from random exchange interactions in gas-poor environments. However, accretion following stellar collisions may break the standard assumption of isotropy in the resulting effective spin distribution. I will present the outcomes of hydrodynamic simulations of collisions between BBHs and stars, focusing on the conditions that potentially lead to spin-orbit alignment. This work sheds light on previously underexplored processes that shape the effective spin distribution of black holes in dense environments.