Inspiral-inherited ringdown tails

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 quasicircular 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 behavior as an integral over the whole inspiral history, we derive an analytical expression that reproduces the slow relaxation (“tail”) observed in our numerical evolutions, obtained with a hyperboloidal compactified grid, for a given noncircular 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 noncircular 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 black hole, with small tangential and radial velocities soon before the plunge. As we corroborate with semianalytical 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 nonlinear evolutions and possible observational consequences. We also briefly comment on the scattering scenario and on the connection with the soft graviton theorem.