Black-Hole Ringdown from Photon-Sphere Modes in an Elastic Analogue

Abstract

Quasinormal modes (QNMs) govern the ringdown of black holes, yet their physical origin and experimental accessibility remain limited. Here we create an elastic analogue of a black hole using a curved metallic shell engineered to emulate a Schwarzschild-like metric, and directly probe its vibrational dynamics in the time domain. Following impulsive excitation, the elastic system exhibits a clear ringdown response, providing a tangible analogue of black-hole ringing. The underlying modes are flexural vibrations localized near the photon sphere. A reduction of the thin-shell elastic equations yields a photon-sphere effective potential and predicts the dependence of the localized-mode frequencies on azimuthal order. Crucially, they persist even when boundary reflections are strongly suppressed, demonstrating that their confinement is governed by a curvature-induced effective potential rather than by cavity boundaries. This platform enables direct access to quasinormal modes through both their temporal decay and spectral signatures, establishing a direct connection between photon-sphere dynamics and ringdown. More broadly, our results identify curvature-induced trapping as a general mechanism for wave localization and dissipation in open systems.