Ergoregion instability: The hydrodynamic vortex

TL;DR

This paper investigates the ergoregion instability in a hydrodynamic vortex, an experimental analog of astrophysical ergoregions, revealing insights into superradiant mechanisms without horizons.

Contribution

It provides a detailed analysis of ergoregion instability in a laboratory-analog hydrodynamic vortex, bridging theoretical predictions with experimental realizations.

Findings

Demonstrates the presence of ergoregion instability in the hydrodynamic vortex.

Analyzes superradiant amplification mechanisms in the vortex setup.

Provides potential pathways for laboratory experiments to study black hole analogs.

Abstract

Four-dimensional, asymptotically flat spacetimes with an ergoregion but no horizon have been shown to be linearly unstable against a superradiant-triggered mechanism. This result has wide implications in the search for astrophysically viable alternatives to black holes, but also in the understanding of black holes and Hawking evaporation. Here we investigate this instability in detail for a particular setup which can be realized in the laboratory: the {\it hydrodynamic vortex}, an effective geometry for sound waves, with ergoregion and without an event horizon.