Inspiral-inherited ringdown tails

TL;DR

This paper analytically and numerically investigates the late-time relaxation (tails) of perturbed Schwarzschild black holes, revealing how orbital eccentricity enhances tail signals and implications for gravitational wave observations.

Contribution

It provides an analytical model for black hole tail relaxation that accounts for complex orbital dynamics and explains tail enhancement in eccentric binaries.

Findings

The late-time tail is a superposition of power-laws, with the slowest being Price's law.

Eccentric orbits significantly amplify tail signals, especially near plunge.

Tail amplitudes can be accurately extracted from late inspiral stages even for high eccentricities.

Abstract

We study the late-time relaxation of a perturbed Schwarzschild black hole, driven by a source term representing an infalling particle in generic orbits. We consider quasi-circular and eccentric binaries, dynamical captures and radial infalls, with orbital dynamics driven by an highly accurate analytical radiation reaction. After reviewing the description of the late-time behaviour as an integral over the whole inspiral history, we derive an analytical expression exactly reproducing the slow relaxation observed in our numerical evolutions, obtained with a hyperboloidal compactified grid, for a given particle trajectory. We find this signal to be a superposition of an infinite number of power-laws, the slowest decaying term being Price's law. Next, we use our model to explain the several orders-of-magnitude enhancement of tail terms for binaries in non-circular orbits, shedding light on recent unexpected results obtained in numerical evolutions. In particular, we show the dominant terms controlling the enhancement to be activated when the particle is far from the BH, with small tangential and radial velocities soon before the plunge. As we corroborate with semi-analytical calculations, this implies that for large eccentricities the tail amplitude can be correctly extracted even when starting to evolve only from the last apastron before merger. We discuss the implications of these findings on the extraction of late-time tail terms in non-linear evolutions, and possible observational consequences. We also briefly comment on the scattering scenario, and on the connection with the soft graviton theorem.