UCLA

Almost every galaxy, including the Milky Way, has a supermassive black hole (SMBH) at its center. Surrounding these SMBHs are dense environments of stars and stellar relics. One consequence of this dense environment is that stars and stellar remnants frequently interact with one another. This dissertation examines how these interactions lead to unique populations of stars, binaries, and black holes. This work is undertaken in four studies, the first of which focuses on binary systems in the presence of a distant perturber. Most massive stars reside in triple systems or higher order multiples. Similarly, any binary system in the Galactic Center forms a triple system with the central SMBH. Any binary system that resides in the nuclear star cluster will be gravitationally perturbed by the SMBH, just as the tertiary star in a stellar triple will gravitationally perturb the two inner stars. These perturbations can alter the orbital parameters. In Rose et al. (2019), I examine the observational signatures of these gravitational interactions. Specifically, I show that the binary birth configurations are an excellent predictor of the final orbits; we can use observations of older stellar populations to learn about their birth conditions. Additionally, my work predicts that perturbations from the third body will cause many binaries to merge. However, binary evolution in a star cluster is further complicated by the densely populated surroundings. In particular, interactions and collisions with surrounding objects can destroy binary systems. A surviving binary can therefore place a density constraint on its environment. I illustrate this procedure in Rose et al. (2020), showing that an observed binary has implications for the number of compact objects in its vicinity. Generally, the dynamics of a galactic nucleus means that binary systems become fewer over time, either due to third-body induced mergers or interactions with stars in the surrounding cluster, and singles should dominate an older population. Collisions, however, will continue to shape the population of singles, in particular by making more massive objects. Collisions between black holes (BHs) and stars, for example, represent a promising channel to form intermediate-mass BHs (Rose et al. 2022), while main-sequence stellar collisions can produce more massive, rejuvenated stars (Rose et al. 2023). The former may explain the origins of black holes above the maximum mass predicted by stellar evolution models: over many collisions with stars, the BH accretes enough material to grow appreciably in size.