Presentation #301.02 in the session Compact Object Binaries II: Cluster Environments.
Stars and stellar remnants are concentrated in the inner parsec of a galactic center, which harbors a supermassive black hole (SMBH). In this dense environment, compact objects can collide and interact with main-sequence stars, the most populous objects there. I will discuss the implications and applications of collisions in a galactic nucleus (GN). For example, during a collision, a stellar-mass black hole (BH) can accrete mass. Over many collisions, it can grow to ten or a hundred times its initial size. Repeated BH-star collisions therefore represent a formation channel for intermediate-mass black holes (IMBHs), with implications for gravitational wave (GW) sources. In the dense GN environment, BHs and IMBHs can migrate and merge with the SMBH via dynamical friction and two-body relaxation. These frequent events, extreme mass ratio inspirals (EMRIs) and intermediate-mass ratio inspirals (IMRIs), emit GWs. Compact object collisions with stars can also produce electromagnetic signatures. A GN is therefore an ideal environment for the creation of extreme transient events like GW and X-ray sources.