# Backreaction in an analogue black hole experiment

## TL;DR

This paper demonstrates that a fluid analogue of a black hole can exhibit backreaction effects, where the system's global parameters evolve due to scattering processes, enabling the study of dynamic black hole spacetimes in laboratory settings.

## Contribution

It introduces a rotating draining vortex flow model showing that fluid systems can exhibit backreaction effects, linking scattering processes to global parameter changes.

## Key findings

- Memory effect encodes scattering in the total mass of the system.
- Backreaction causes significant global changes in background parameters.
- Dynamical metric captures wave-background interactions in evolving black hole analogues.

## Abstract

In general relativity, the interaction between a black hole and the fields around it (a process known as backreaction) proceeds via the evolution of the black holes mass and angular momentum. Analogue models of gravity, particularly fluid mechanical analogues, have been very successful in mimicking the propagation of fields, and the effects they experience, around black holes. However, hydrodynamic black holes are externally driven systems whose effective mass and angular momentum are set by experimental parameters, and as such no significant internal backreaction processes are expected to take place. We show, using a rotating draining vortex flow, that a fluid system of finite size exhibits a memory that keeps track of scattering processes in the system. This memory is encoded in the total mass of the system and hence, the backreaction arises as a significant global change in the background parameters, as opposed to a small local correction. More importantly, this backreaction is encapsulated by a dynamical metric, raising the possibility of studying wave-background interaction around evolving black hole spacetimes.