Princeton University Gravity Initiative Seminar

Abstract: The Laser Interferometer Space Antenna is a planned space-based detector that will measure gravitational waves in the milli-hertz regime. One of the primary targets for LISA is an extreme mass ratio inspiral (EMRI), where a stellar mass compact object (SMCO) on a bound orbit slowly inspirals into a supermassive black hole (SMBH) due to the loss of energy to gravitational waves. EMRIs can spend upwards of a million wave cycles in the LISA band and serve as excellent probes of the environment of the SMBH they orbit.  

For actively accreting supermassive black holes with thin disks, the SMCO can exchange energy and angular momentum with the disk and leave potentially measurable signatures in the LISA band. While the disk-EMRI interaction is reminiscent of the classical planet-disk interaction studied in protoplanetary literature, the close vicinity of the SMCO to the SMBH introduces strong relativistic effects that can alter the nature of the interaction. In this talk, I will describe a simple toy model that can be used to understand some basic features of the interaction by modeling the interaction as a three-body problem. I will show that strong relativistic precession effects can cause a significant difference in the disc-EMRI interaction close to a SMBH and can potentially lead to a change in the direction of the torque on the SMCO. Finally, I will also discuss the amount of dephasing the disk-EMRI interaction causes in the LISA band and highlight how LISA could potentially constrain the properties of accretion disks close to SMBHs.