On the origin of quasinormal modes in semi-open systems

TL;DR

This paper investigates how the quasinormal mode spectrum of black hole analogues transitions from open to finite-sized systems by introducing a partially reflecting boundary, revealing continuous spectral changes and easier excitation via noise.

Contribution

It demonstrates a continuous connection between open and finite-sized QNM spectra and shows that QNMs can be readily excited by background noise in laboratory analogues.

Findings

QNM spectrum varies continuously with boundary reflectivity.

QNM excitation is facilitated by incoherent background noise.

Finite-sized systems can mimic open-system QNM behavior.

Abstract

Astrophysical black holes are open systems which, when perturbed, radiate quasi-normal modes (QNMs) to infinity. By contrast, laboratory analogues are necessarily finite-sized, presenting a potential obstacle to exciting QNMs in experiments. We explore how the QNM spectrum of a toy-model black hole changes when enclosed by a partially reflecting wall with adjustable reflectivity. Our results reveal a continuous connection between the QNM spectra of open and finite-sized systems. Additionally, we demonstrate that QNMs in this setup are easily excited by incoherent background noise. This work opens new avenues for studying QNMs of black holes and compact objects in laboratory settings, where finite-size effects and noise are unavoidable.