Dynamics and Transients Form Galactic Centers

The centers of most galaxies harbor supermassive black holes orbited by millions of stars and, likely, thousands of stellar-mass black holes. Gravitational scattering drives mass segregation: the heavier stars and black holes sink toward the center and dominate the dynamics of the innermost region. Consequently, massive stars should be overrepresented among tidal disruption events (TDEs). Stellar collisions may deplete the population of ordinary stars in the inner light year, while disruption of binaries can replenish this region with new stars. In the innermost region, the concentration of compact objects may enable the space-based gravitational-wave observatory LISA to detect thousands of stellar-mass black holes in galactic nuclei. We confront these predictions with observations of stars in our own Galactic Center and show how the recently detected quasi-periodic X-ray eruptions may provide a new probe of the dynamics of stars near supermassive black holes.