Photon surfaces in spherically, planar, and hyperbolically symmetric spacetimes in D dimensions: Sonic point/photon sphere correspondence

Sonic point/photon sphere (SP/PS) correspondence is a theoretical phenomenon which appears in fluid dynamics on curved spacetime and its existence has been recently proved in quite wide situations as theorems. The theorems state that a sonic point (SP) of radiation fluid flow must be on an unstable photon sphere (PS) when the fluid flows radially or rotationally on an equatorial plane in spherically symmetric spacetime of arbitrary dimensions. In this paper, we investigate SP/PS correspondence in spherically, planar, and hyperbolically symmetric spacetime. As the corresponding objects of photon spheres in nonspherically symmetric spacetime, we consider photon surfaces introduced by Claudel et al. (2001) in the spacetime. After formulating the problem of radial fluid flows, we prove there always exists a correspondence between the sonic points and the photon surfaces, namely, SP/PS correspondence in nonspherically symmetric spacetime.