Lecturer: Nicholas Stone, (Columbia) Abstract: In most regions of the Universe, stars follow orbits in the smooth background potentials of their host galaxies, and populations of stars evolve according to the collisionless Boltzmann equation. However, in the densest stellar systems, such as open, globular, and nuclear star clusters, two body scatterings create granularities in the background potential, and populations of stars evolve via the collisional Boltzmann equation, relaxing into steady state configurations in less than the age of the Universe. I study these dense stellar environments from a primarily theoretical perspective, and will discuss how collisional relaxation and close encounters between stars and compact objects can create many extreme astrophysical phenomena. In this talk, I will discuss some of the rare sources of electromagnetic and gravitational radiation produced by close encounters, such as X-ray binaries and LIGO-band black hole mergers. However, I will focus especially on the tidal disruption events (TDEs) that occur in galactic nuclei. During a TDE, the star is ripped apart by the tidal field of a supermassive black hole, and dissipation in the stellar debris powers a luminous flare brighter than most supernovae and visible across the entire electromagnetic spectrum. Dozens of TDE flares have been discovered at optical, UV, and X-ray wavelengths in the last decade, and upcoming time domain surveys (such as ZTF, LSST, and eROSITA) will discover thousands more. Properly interpreted, a large sample of these flares holds great promise for testing questions in accretion physics and measuring the demography of quiescent supermassive black holes. I will discuss the dynamical processes that set tidal disruption event rates and the leading order role general relativity plays in accretion of tidal debris, as well as ways in which black hole spin may be imprinted into TDE observables.