EMRIs in Kerr Spacetime: The Role of Inclination Diffusion

Extreme mass ratio inspirals (EMRIs) are expected to be a major source of gravitational waves (GWs) for the future Laser Interferometer Space Antenna (LISA). An EMRI occurs when a compact object slowly inspirals into a massive black hole (MBH), driven by the emission of gravitational radiation. The classical formation channel involves repeated two-body interactions within dense nuclear star clusters. However, both the event rates and orbital parameters of EMRIs remain highly uncertain. A major source of this uncertainty is the poorly constrained ratio between gradual inspiral EMRIs and direct plunges, which do not produce detectable GWs. While almost all studies of astrophysical EMRI production focus on the Schwarzschild limit, one previous work examining the Kerr metric found that the spin of the central MBH can significantly affect the EMRI-to-plunge ratio, by up to a factor of ~30.  The Kerr rate enhancement depends strongly on orbital inclination; however, this past work held inclination fixed.  In reality, close encounters with other stars can cause an object's inclination to change over time, potentially turning a detectable EMRI into a plunge, or vice versa. In this talk, I will present my work on EMRI rates around spinning MBHs when allowing the inclination of the object to evolve between orbits. This study aims to improve our understanding of EMRI rates and the distribution of their parameters observable by LISA.