`Superresonance' from a rotating acoustic black hole

TL;DR

This paper demonstrates that sound waves reflecting off a rotating fluid vortex analogous to a black hole can be amplified within certain frequency ranges, suggesting potential observable superresonance effects in superfluid systems.

Contribution

It introduces a model linking acoustic vortices to black hole physics, showing sound wave amplification (superresonance) in a rotating fluid vortex analogy.

Findings

Sound waves are amplified upon reflection from the vortex.

Amplification depends on the wave frequency and vortex angular velocity.

Potential observation in superfluid systems like liquid HeII.

Abstract

Using the analogy between a shrinking fluid vortex (`draining bathtub'), modelled as a (2+1) dimensional fluid flow with a sink at the origin, and a rotating (2+1) dimensional black hole with an ergosphere, it is shown that a scalar sound wave is reflected from such a vortex with an {\it amplification} for a specific range of frequencies of the incident wave, depending on the angular velocity of rotation of the vortex. We discuss the possibility of observation of this phenomenon, especially for inviscid fluids like liquid HeII, where vortices with quantized angular momentum may occur.