# Analogue Black Hole Spectroscopy; or, how to listen to dumb holes

## TL;DR

This paper introduces a novel spectroscopy-based method to analyze vortex flows in fluids by drawing analogies with black hole physics, enabling non-invasive flow measurement through characteristic emission spectra.

## Contribution

It develops a new technique applying black hole spectroscopy methods to identify vortex flows via their ringdown spectra, expanding the fluid-gravity analogy.

## Key findings

- Successful identification of vortex flows through spectral analysis.
- Demonstration of the analogy between vortex ringdown and black hole relaxation.
- Potential for non-invasive flow diagnostics in fluids and superfluids.

## Abstract

Spectroscopy is a fundamental tool in science which consists in studying the response of a system as a function of frequency. Among its many applications in Physics, Biology, Chemistry and other fields, the possibility of identifying objects and structures through their emission spectra is remarkable and incredibly useful. In this paper we apply the spectroscopy idea to a numerically simulated hydrodynamical flow, with the goal of developing a new, non-invasive flow measurement technique. Our focus lies on an irrotational draining vortex, which can be seen, under specific conditions, as the analogue of a rotating black hole (historically named a dumb hole). This paper is a development of a recent experiment that suggests that irrotational vortices and rotating black holes share a common relaxation process, known as the ringdown phase. We apply techniques borrowed from black hole physics to identify vortex flows from their characteristic spectrum emitted during this ringdown phase. We believe that this technique is a new facet of the fluid-gravity analogy and constitutes a promising way to investigate experimentally vortex flows in fluids and superfluids alike.