Inspiral into Gargantua

TL;DR

This paper models the inspiral of a compact object into a near-extremal rotating black hole, revealing unique gravitational wave signatures that could confirm the existence of such black holes.

Contribution

It introduces a model predicting a constant-frequency gravitational wave signal during near-horizon inspiral into near-extremal black holes, contrasting with typical chirping signals.

Findings

Gravitational radiation exhibits a constant frequency equal to twice the horizon frequency.

The waveform shows an exponentially damped profile in the near-horizon regime.

Detection of this signal would indicate a near-extremal black hole presence.

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.