Quasinormal Mode Excitation in the Horizon Shear of Near-Extremal Kerr Black Holes
Abstract
The horizon shear of a near-extremal Kerr black hole perturbed by an eccentric extreme mass ratio inspiral shows low amplitude, high frequency oscillations (''wiggles") after periapsis passage. Previous works are unable to tie the frequency of the wiggles to the orbit, and argue they cannot be quasinormal modes (QNMs). We show that they are Kerr QNMs belonging to the damped-mode branch --- that is, modes whose decay rate stays finite as the spin approaches extremality. For an equatorial prograde orbit with p = 3M and e = 0.85 and spins ranging from a/M = 0.999 to a/M = 0.99999, fits to the time-domain shear identify the fundamental (ℓ,m) = (2,1) and (3,2) modes as the dominant and first subdominant excitations. Fitting each multipole separately gives frequencies to within two standard deviations of the Kerr values and provides evidence for the excitation of the fundamental (3,1), (4,1) and (4,2) modes, though these are not resolvable in the full signal. We further argue that the same wiggles must be present in the tidal field that drives the shear. For ℓ ≤ 4 we find no evidence of QNM excitation in the m = 0 or the m = ℓ multipoles.
Related
- Complete quasinormal modes of Type-D black holes. II. Extremal Kerr black holes
- Quasinormal modes of Schwarzschild--AdS black holes with a near-horizon reflective surface
- Black hole quasinormal mode excitation and mixing for coupled fields
- Extremal black hole throats from non extremal near horizon expansions
- Stationary scalar clouds, quasinormal ringing, and observational signatures of (near-)extremal rotating Kalb–Ramond black holes: from the superradiant threshold to EHT bounds
BibTeX
@misc{black2026quasinormal,
title = {{Quasinormal Mode Excitation in the Horizon Shear of Near-Extremal Kerr Black Holes}},
author = {Brennen Black},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.39729},
eprint = {2610.39729},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.39729},
}
RIS
TY - UNPB
TI - Quasinormal Mode Excitation in the Horizon Shear of Near-Extremal Kerr Black Holes
AU - Brennen Black
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2610.39729
UR - https://arxiv.org/abs/2610.39729
AB - The horizon shear of a near-extremal Kerr black hole perturbed by an eccentric extreme mass ratio inspiral shows low amplitude, high frequency oscillations (''wiggles") after periapsis passage. Previous works are unable to tie the frequency of the wiggles to the orbit, and argue they cannot be quasinormal modes (QNMs). We show that they are Kerr QNMs belonging to the damped-mode branch --- that is, modes whose decay rate stays finite as the spin approaches extremality. For an equatorial prograde orbit with p = 3M and e = 0.85 and spins ranging from a/M = 0.999 to a/M = 0.99999, fits to the time-domain shear identify the fundamental (ℓ,m) = (2,1) and (3,2) modes as the dominant and first subdominant excitations. Fitting each multipole separately gives frequencies to within two standard deviations of the Kerr values and provides evidence for the excitation of the fundamental (3,1), (4,1) and (4,2) modes, though these are not resolvable in the full signal. We further argue that the same wiggles must be present in the tidal field that drives the shear. For ℓ ≤ 4 we find no evidence of QNM excitation in the m = 0 or the m = ℓ multipoles.
ER -