High Energy2026-07-312 minarXiv:2607.29273expressBlack Hole Echo: What the Horizon Sounds LikeWhen two black holes merge, ripples spread across the fabric of spacetime — gravitational waves. But what if one of them isn't a run-of-the-mill black hole but something else — an exotic compact object?Corentin Guigotno-hair theoremFirst law of black hole mechanicsJacob BekensteinJohn Archibald WheelerStephen Hawkingblack hole mergergravitational wavesevent horizonblack holegravitational singularity👍👎☆SimplePopularAdvanced