Listening to the Horizon: Probing Near-Horizon Reflectivity with GW250114
Abstract
Testing the horizon properties of astrophysical black holes is a central goal of gravitational-wave astronomy. The recently identified Direct Wave (DW), a prompt non-quasinormal component of GW250114, provides a new probe of near-horizon physics. While it remains unclear whether the DW itself carries horizon information, we show that it enables a novel null test of horizon reflectivity. If the remnant is an exotic compact object (ECO) with a partially reflecting surface, inward plunge radiation is reflected and leaks back through the gravitational potential barrier, producing a delayed DW echo whose amplitude is set by the surface reflectivity (|ℛs|). We construct the corresponding echo template, normalized by the observed DW, and search for it in quasinormal-mode-filtered data. We find no evidence for an echo (lnℬ=−2.9) and obtain the 90\% credible bound |ℛs|<0.06, corresponding to a reflected energy fraction below 0.4%, for surfaces from 0.1 Mf to a Planck length from the would-be horizon. Our method thus turns the prompt ringdown signal into a direct test of horizon reflectivity.
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BibTeX
@misc{prasad2026listening,
title = {{Listening to the Horizon: Probing Near-Horizon Reflectivity with GW250114}},
author = {R. Prasad and Subhodeep Sarkar and Sudipta Sarkar},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.12429},
eprint = {2610.12429},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.12429},
}
RIS
TY - UNPB
TI - Listening to the Horizon: Probing Near-Horizon Reflectivity with GW250114
AU - R. Prasad
AU - Subhodeep Sarkar
AU - Sudipta Sarkar
PY - 2026
DA - 2026/10/08
PB - arXiv
DO - 10.48550/arxiv.2610.12429
UR - https://arxiv.org/abs/2610.12429
AB - Testing the horizon properties of astrophysical black holes is a central goal of gravitational-wave astronomy. The recently identified Direct Wave (DW), a prompt non-quasinormal component of GW250114, provides a new probe of near-horizon physics. While it remains unclear whether the DW itself carries horizon information, we show that it enables a novel null test of horizon reflectivity. If the remnant is an exotic compact object (ECO) with a partially reflecting surface, inward plunge radiation is reflected and leaks back through the gravitational potential barrier, producing a delayed DW echo whose amplitude is set by the surface reflectivity (|ℛ_s|). We construct the corresponding echo template, normalized by the observed DW, and search for it in quasinormal-mode-filtered data. We find no evidence for an echo (lnℬ=−2.9) and obtain the 90\% credible bound |ℛ_s|<0.06, corresponding to a reflected energy fraction below 0.4%, for surfaces from 0.1 M_f to a Planck length from the would-be horizon. Our method thus turns the prompt ringdown signal into a direct test of horizon reflectivity.
ER -