Fermat's principle in black-hole spacetimes

Abstract

Black-hole spacetimes are known to possess closed light rings. We here present a remarkably compact theorem which reveals the physically intriguing fact that these unique null circular geodesics provide the {\it fastest} way, as measured by asymptotic observers, to circle around spinning Kerr black holes.

5 pages. This essay received an Honorable Mention in the 2018 Essay Competition of the Gravity Research Foundation

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