Inspiral into Gargantua

Abstract

We model the inspiral of a compact object into a more massive black hole rotating very near the theoretical maximum. We find that once the body enters the near-horizon regime the gravitational radiation is characterized by a constant frequency, equal to (twice) the horizon frequency, with an exponentially damped profile. This contrasts with the usual 'chirping' behavior and, if detected, would constitute a 'smoking gun' for a near-extremal black hole in nature.