Black-hole spectroscopy from a giant quantum vortex

TL;DR

This paper demonstrates black-hole-like quasinormal modes in superfluid helium-4 with a giant quantum vortex, enabling laboratory black-hole spectroscopy through noise-driven interface waves.

Contribution

It shows that multiple quasinormal modes can be extracted from superfluid helium-4 vortex systems, providing a new laboratory platform for black-hole spectroscopy.

Findings

Multiple QNMs are excited and can be resolved in the superfluid system.

Fundamental modes and overtones oscillate at frequencies related to system size.

QNM spectrum shifts in finite systems enhance detectability.

Abstract

Black-hole spectroscopy aims to infer the fundamental properties of black holes by analysing the spectrum of gravitational waves emitted as they settle into equilibrium. These resonances, known as quasinormal modes (QNMs), decay rapidly, which limits the time-domain analysis of gravitational-wave data or numerical simulations to the longest-lived mode, except for a particularly loud event. Owing to the analogy between fields in curved spacetime and waves propagating in a flowing medium, QNMs can be equally excited in a laboratory. In these finite-sized systems, the QNM spectrum is expected to alter: compared to their counterparts in unbounded settings, the real frequencies of QNMs shift while their damping rates (imaginary frequencies) reduce, thereby enhancing their detectability. Here we show that multiple QNMs can be extracted from noise-driven interface waves surrounding a giant quantum vortex in superfluid helium-4, which emulates a spacetime geometry indicative of a rotating black hole. By resolving waves with different azimuthal periodicity, we find that both fundamental modes and their higher-frequency overtones are excited, and oscillate at frequencies given by the size of our system. Since similar effects may arise in astrophysical scenarios due to the interstellar medium or dark matter, gravity simulators now complement numerical and observational approaches to black-hole spectroscopy.