paper

The geometry of photon surfaces

arXiv:gr-qc/0005050 · doi:10.1063/1.1308507

Abstract

The photon sphere concept in Schwarzschild space-time is generalized to a definition of a photon surface in an arbitrary space-time. A photon sphere is then defined as an SO(3)xR-invariant photon surface in a static spherically symmetric space-time. It is proved, subject to an energy condition, that a black hole in any such space-time must be surrounded by a photon sphere. Conversely, subject to an energy condition, any photon sphere must surround a black hole, a naked singularity or more than a certain amount of matter. A second order evolution equation is obtained for the area of an SO(3)-invariant photon surface in a general non-static spherically symmetric space-time. Many examples are provided.

24 pages, 5 figures. Uses the following packages: amsmath, amsthm, amssymb, amsfonts, mathrsfs, enumerate, graphicx

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