Institute for Advanced Study Astrophysics Seminar

Massive black holes (MBHs) exist at the centers of many dense star systems, particularly in galactic nuclei.  Steady accretion onto MBHs powers active galactic nuclei, but dynamical processes near MBHs can generate various forms of transient radiation.  In particular, the excitation of stars and compact objects onto high-eccentricity orbits allows for close interactions with the MBH that produce bursts of either electromagnetic radiation (e.g. tidal disruption events, or TDEs) or gravitational wave radiation (e.g. extreme mass ratio inspirals, or EMRIs).  The region of phase space corresponding to such processes is known as the loss cone, and the dense, collisional environments of galactic nuclei are characterized by steady loss cone repopulation due to weak, two-body scatterings.  Loss cone refilling and transient (TDE/EMRI) production rates have thus been traditionally studied as a diffusive process.  I will review the classic dynamical theory of the loss cone, and then present recent developments that have examined the role of non-diffusive processes in producing loss cone transients.  Specifically, I will present recent work on strong scatterings, which generally reduce the rate of TDEs and EMRIs, but also on non-perturbative gravitational wave emission, which may increase EMRI rates through the novel "cliffhanger" phenomenon.