Gravitational waves from a plunge into a nearly extremal Kerr black hole

TL;DR

This paper numerically investigates gravitational waves from a plunge into nearly extremal Kerr black holes, revealing a transient inverse time decay in the ringdown phase that transitions to exponential decay, with implications for gravitational wave detection.

Contribution

It provides the first detailed numerical analysis of gravitational wave signals from plunges into nearly extremal Kerr black holes, highlighting a transient decay behavior in the ringdown phase.

Findings

Transient inverse time decay in ringdown observed

Transition to exponential decay depends on black hole spin

Potential gravitational wave sources for observatories

Abstract

We study numerically in the time domain the linearized gravitational waves emitted from a plunge into a nearly extremal Kerr black hole by solving the inhomogeneous Teukolsky equation. We consider spinning black holes for which the specific spin angular momentum $a/M=1-\epsilon$, and we consider values of $\epsilon\geq 10^{-6}$. We find an effective transient behavior for the quasi-normal ringdown: the early phase of the quasi-normal ringdown is governed by a decay according to inverse time, with frequency equaling twice the black hole's horizon frequency. The smaller $\epsilon$ the later the transition from this transient inverse time decay to exponential decay. Such sources, if exist, may be interesting potential sources for terrestrial or space borne gravitational wave observatories.