Relativistic acoustic geometry

Abstract

Sound wave propagation in a relativistic perfect fluid with a non-homogeneous isentropic flow is studied in terms of acoustic geometry. The sound wave equation turns out to be equivalent to the equation of motion for a massless scalar field propagating in a curved spacetime geometry. The geometry is described by the acoustic metric tensor which depends locally on the equation of state and the 4-velocity of the fluid. For a relativistic supersonic flow in curved spacetime the ergosphere and acoustic horizon may be defined in a way analogous to the non-relativistic case. A general-relativistic expression for the acoustic analogue of surface gravity has been found.