Black hole quasibound states from a draining bathtub vortex flow

TL;DR

This paper presents a hydrodynamic analogue of a rotating black hole using a draining bathtub vortex flow, revealing how vorticity influences quasinormal modes and leads to long-lived quasibound states, with potential for experimental testing.

Contribution

It introduces a novel hydrodynamic model simulating a rotating black hole, demonstrating the impact of vorticity on quasinormal mode spectra and quasibound states.

Findings

Vorticity induces a scalar field with an effective mass in the vortex core.

The spectrum includes long-lived trapped quasibound states.

The model can be tested in future analogue gravity experiments.

Abstract

Quasinormal modes are a set of damped resonances that describe how an excited open system is driven back to equilibrium. In gravitational physics these modes characterise the ringdown of a perturbed black hole, e.g. following a binary black hole merger. A careful analysis of the ringdown spectrum reveals the properties of the black hole, such as its angular momentum and mass. In more complex gravitational systems the spectrum might depend on more parameters, and hence allows us to search for new physics. In this letter we present a hydrodynamic analogue of a rotating black hole, that illustrates how the presence of extra structure affects the quasinormal mode spectrum. The analogy is obtained by considering wave scattering on a draining bathtub vortex flow. We show that due to vorticity of the background flow, the resulting field theory corresponds to a scalar field on an effective curved spacetime which acquires a local mass in the vortex core. The obtained quasinormal mode spectrum exhibits long-lived trapped modes, commonly known as quasibound states. Our findings can be tested in future experiments, building up on recent successful implementations of analogue rotating black holes.