Analog rotating black holes in a magnetohydrodynamic inflow

TL;DR

This paper models analog black hole geometries in magnetohydrodynamic flows, revealing how magnetic pressure influences the effective spacetime structures and classifying different types of magnetoacoustic geometries.

Contribution

It introduces a magnetoacoustic metric for fast MHD modes in MHD flows and classifies the resulting analog spacetimes based on flow parameters.

Findings

Magnetoacoustic geometry can mimic rotating black holes, ergoregions, and spinning stars.

Magnetic pressure significantly affects the properties of the effective geometries.

Fast MHD modes can be described by a magnetoacoustic metric in certain flow conditions.

Abstract

We present a model of the analog geometry in a magnetohydrodynamic (MHD) flow. For the MHD flow with magnetic pressure-dominated and gas pressure-dominated conditions, we obtain the magnetoacoustic metric for the fast MHD mode. For the slow MHD mode, on the other hand, the wave is governed by the advective-type equation without an isotropic dispersion term. Thus, the "distance" perpendicular to the wave propagation is not defined and the magnetoacoustic metric cannot be introduced. To investigate the properties of the magnetoacoustic geometry for the fast mode, we prepare a two-dimensional axisymmetric inflow and examine the behavior of magnetoacoustic rays which is a counterpart of the MHD waves in the eikonal limit. We find that the magnetoacoustic geometry is classified into three types depending on two parameters characterizing the background flow:~analog spacetimes of rotating black holes, ultra spinning stars with ergoregions, and spinning stars without ergoregions. We address the effects of the magnetic pressure on the effective geometries.