Onset of superradiant instabilities in the hydrodynamic vortex model

Understand

The hydrodynamic vortex, an effective spacetime geometry for propagating sound waves, is studied analytically.

• In contrast with the familiar Kerr black-hole spacetime, the hydrodynamic vortex model is described by an effective acoustic geometry which has no horizons.
• However, this acoustic spacetime possesses an ergoregion, a property which it shares with the rotating Kerr spacetime.
• It has recently been shown numerically that this physical system is linearly unstable due to the superradiant scattering of sound waves in the ergoregion of the effective spacetime.