Extreme-mass ratio inspirals around a spinning horizonless compact object

Abstract

"Extreme mass-ratio inspirals detectable by LISA are unique probes of the nature of supermassive compact objects. We compute the gravitational-wave signal emitted by a point particle in a circular equatorial orbit around a Kerr-like horizonless object defined by an effective radius and a reflectivity coefficient. Teukolsky equations are solved consistently with suitable boundary conditions, and the modified energy fluxes are used to evolve the orbital parameters adiabatically. We show that the gravitational fluxes have resonances corresponding to the low-frequency quasinormal modes of the central object, which can contribute significantly to the gravitational-wave phase. Overall, the absence of a classical event horizon in the central object affects the gravitational-wave signal dramatically, with deviations even larger than those previously estimated by a model-independent analysis of the tidal heating. Talk based on: Elisa Maggio, Maarten van de Meent, Paolo Pani, in preparation"