Early-time tails in Kerr black hole ringdown
Abstract
Black hole ringdowns are modelled as a superposition of quasinormal modes (QNMs), although the branch cut of the Green's function produces a nonoscillatory tail that may contaminate early-time ringdown analyses. Within linear perturbation theory, we quantify this branch-cut contribution for the scattering of localised Gaussian wave packets by a Kerr black hole with mass M. Defining the onset of ringdown as the earliest time at which the QNM and branch-cut contributions reconstruct the waveform, we evaluate the branch-cut amplitude relative to the QNM amplitude. For wave packets with a characteristic frequency ω0∼ 1/M, the branch-cut amplitude is typically of order 10% of the QNM amplitude at ringdown onset with only a mild dependence on spin. We further find that the tail waveform before convolving with a source is almost independent of spin. The spin dependence of the relative amplitude therefore resides primarily in the excitation of the QNMs. Our results suggest that the branch-cut contribution may affect the accuracy of black hole spectroscopy, particularly near the onset of ringdown.
Related
- Dynamics, ringdown, and accretion-driven multiple quasi-periodic oscillations of Kerr–Bertotti–Robinson black holes
- Theoretical Aspects of Direct Waves in Kerr Black Holes: Pole-Splitting Method for Ringdown Analysis
- Time-domain analysis of scalar perturbations of Kerr--Newman black holes with Chern--Simons and Maxwell couplings
- Exact Cancellation of Horizon Modes in Kerr Ringdown
- From driven oscillations to free ringdown: a particle plunging into Kerr
BibTeX
@misc{gupta2026earlytime,
title = {{Early-time tails in Kerr black hole ringdown}},
author = {Ansh Gupta and Naritaka Oshita},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.39058},
eprint = {2610.39058},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.39058},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Early-time tails in Kerr black hole ringdown
AU - Ansh Gupta
AU - Naritaka Oshita
PY - 2026
DA - 2026/10/28
PB - arXiv
DO - 10.48550/arxiv.2610.39058
UR - https://arxiv.org/abs/2610.39058
AB - Black hole ringdowns are modelled as a superposition of quasinormal modes (QNMs), although the branch cut of the Green's function produces a nonoscillatory tail that may contaminate early-time ringdown analyses. Within linear perturbation theory, we quantify this branch-cut contribution for the scattering of localised Gaussian wave packets by a Kerr black hole with mass M. Defining the onset of ringdown as the earliest time at which the QNM and branch-cut contributions reconstruct the waveform, we evaluate the branch-cut amplitude relative to the QNM amplitude. For wave packets with a characteristic frequency ω_0∼ 1/M, the branch-cut amplitude is typically of order 10% of the QNM amplitude at ringdown onset with only a mild dependence on spin. We further find that the tail waveform before convolving with a source is almost independent of spin. The spin dependence of the relative amplitude therefore resides primarily in the excitation of the QNMs. Our results suggest that the branch-cut contribution may affect the accuracy of black hole spectroscopy, particularly near the onset of ringdown.
ER -