Complex frequency evolution of direct waves from binary black hole mergers
Abstract
While no signal originating at a black hole's event horizon can reach future null infinity, information about the horizon and its immediate vicinity can be encoded in asymptotic properties of waves emitted by matter or field perturbations falling toward a growing/forming horizon. Within a response-filtered framework, "direct wave" denotes source-sensitive plunge and remnant-formation information revealed by filtering the black-hole response. Unlike a stationary damped sinusoid with a fixed complex frequency, the direct wave follows the evolving source and has an evolving instantaneous complex frequency tied at late times to the remnant horizon angular velocity ΩH and surface gravity κH. Using rational filters, we remove quasinormal modes from numerical-relativity waveforms to study this evolution. Before numerical contamination, trajectories depend on remnant spin: the real frequency evolves toward 2ΩH from above for lower spins (χf≲0.7) and from below for higher spins (χf≳0.7), while the instantaneous decay rate increases, with best-resolved cases approaching the expected value of 3κH. As in particle-plunge results, the horizon-controlled value is approached only at late times, as frame dragging controls near-horizon motion. For χf∼0.7 remnants of non-precessing, comparable-mass binaries, the early-time real frequency is close to 2ΩH because the binary orbital frequency transitions smoothly to the remnant horizon frequency. Finite-time deviations therefore carry information about merger/collapse dynamics rather than undermining the horizon connection. Full direct-wave evolution requires numerical-relativity calibration. We further show that approximate pole-zero pairing in the Kerr response motivates a minimal filter set that suppresses quasinormal-mode features while revealing source-trajectory information.
Related
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BibTeX
@misc{sun2026complex,
title = {{Complex frequency evolution of direct waves from binary black hole mergers}},
author = {Ling Sun and Sizheng Ma and Patrick P. Chen and Andrew Laeuger and Neil Lu and Yanbei Chen},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2608.23209},
eprint = {2608.23209},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.23209},
}
RIS
TY - UNPB
TI - Complex frequency evolution of direct waves from binary black hole mergers
AU - Ling Sun
AU - Sizheng Ma
AU - Patrick P. Chen
AU - Andrew Laeuger
AU - Neil Lu
AU - Yanbei Chen
PY - 2026
DA - 2026/09/19
PB - arXiv
DO - 10.48550/arxiv.2608.23209
UR - https://arxiv.org/abs/2608.23209
AB - While no signal originating at a black hole's event horizon can reach future null infinity, information about the horizon and its immediate vicinity can be encoded in asymptotic properties of waves emitted by matter or field perturbations falling toward a growing/forming horizon. Within a response-filtered framework, "direct wave" denotes source-sensitive plunge and remnant-formation information revealed by filtering the black-hole response. Unlike a stationary damped sinusoid with a fixed complex frequency, the direct wave follows the evolving source and has an evolving instantaneous complex frequency tied at late times to the remnant horizon angular velocity Ω_H and surface gravity κ_H. Using rational filters, we remove quasinormal modes from numerical-relativity waveforms to study this evolution. Before numerical contamination, trajectories depend on remnant spin: the real frequency evolves toward 2Ω_H from above for lower spins (χ_f≲0.7) and from below for higher spins (χ_f≳0.7), while the instantaneous decay rate increases, with best-resolved cases approaching the expected value of 3κ_H. As in particle-plunge results, the horizon-controlled value is approached only at late times, as frame dragging controls near-horizon motion. For χ_f∼0.7 remnants of non-precessing, comparable-mass binaries, the early-time real frequency is close to 2Ω_H because the binary orbital frequency transitions smoothly to the remnant horizon frequency. Finite-time deviations therefore carry information about merger/collapse dynamics rather than undermining the horizon connection. Full direct-wave evolution requires numerical-relativity calibration. We further show that approximate pole-zero pairing in the Kerr response motivates a minimal filter set that suppresses quasinormal-mode features while revealing source-trajectory information.
ER -