Acoustic horizons in axially symmetric relativistic accretion

Abstract

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