Acoustic horizons in axially symmetric relativistic accretion

TL;DR

This paper investigates the acoustic geometry of axially symmetric relativistic accretion flows onto black holes and neutron stars, analyzing sonic points, shocks, and analogue black hole properties.

Contribution

It introduces a detailed analysis of multitransonic accretion flows with shocks, exploring their causal structure and calculating analogue surface gravity and Hawking temperature.

Findings

Presence of acoustic black hole at sonic points

White hole at the shock in the flow

Calculated analogue surface gravity and Hawking temperature

Abstract

Transonic accretion onto astrophysical objects is a unique example of analogue black hole realized in nature. In the framework of acoustic geometry we study axially symmetric accretion and wind of a rotating astrophysical black hole or of a neutron star assuming isentropic flow of a fluid described by a polytropic equation of state. In particular we analyze the causal structure of multitransonic configurations with two sonic points and a shock. Retarded and advanced null curves clearly demonstrate the presence of the acoustic black hole at regular sonic points and of the white hole at the shock. We calculate the analogue surface gravity and the Hawking temperature for the inner and the outer acoustic horizons.