Superradiant scattering from a hydrodynamic vortex

TL;DR

This paper demonstrates that sound waves can be amplified through superradiant scattering in hydrodynamic vortices, revealing analogies with black hole physics and suggesting experimental tests in Bose-Einstein condensates.

Contribution

It shows superradiant scattering occurs in hydrodynamic vortices without a sonic horizon, expanding the understanding of wave amplification in fluid analogues of black holes.

Findings

Sound waves are amplified when scattered from a vortex.

Superradiance occurs without a sonic horizon in hydrodynamic analogues.

Potential experimental realization in Bose-Einstein condensates is proposed.

Abstract

We show that sound waves scattered from a hydrodynamic vortex may be amplified. Such superradiant scattering follows from the physical analogy between spinning black holes and hydrodynamic vortices. However a sonic horizon analogous to the black hole event horizon does not exist unless the vortex possesses a central drain, which is challenging to produce experimentally. In the astrophysical domain, superradiance can occur even in the absence of an event horizon: we show that in the hydrodynamic analogue, a drain is not required and a vortex scatters sound superradiantly. Possible experimental realization in dilute gas Bose-Einstein condensates is discussed.