Detecting Rotational Superradiance in Fluid Laboratories

TL;DR

This paper proposes an experimental setup using fluids and a rotating cylinder to observe rotational superradiance, a phenomenon predicted in black-hole physics but not yet observed, by demonstrating wave amplification and instabilities.

Contribution

It introduces a feasible laboratory experiment to detect rotational superradiance in fluids, bridging astrophysical theory and experimental fluid dynamics.

Findings

Surface and sound waves are amplified around a rotating cylinder.

Two types of instabilities related to superradiance are identified.

The experimental setup is feasible with existing fluid laboratory equipment.

Abstract

Rotational superradiance was predicted theoretically decades ago, and is chiefly responsible for a number of important effects and phenomenology in black-hole physics. However, rotational superradiance has never been observed experimentally. Here, with the aim of probing superradiance in the lab, we investigate the behavior of sound and surface waves in fluids resting in a circular basin at the center of which a rotating cylinder is placed. We show that with a suitable choice for the material of the cylinder, surface and sound waves are amplified. Two types of instabilities are studied: one sets in whenever superradiant modes are confined near the rotating cylinder and the other, which does not rely on confinement, corresponds to a local excitation of the cylinder. Our findings are experimentally testable in existing fluid laboratories and, hence, offer experimental exploration and comparison of dynamical instabilities arising from rapidly rotating boundary layers in astrophysical as well as in fluid dynamical systems.