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Abstract:
In Schwarzschild spacetime the value r = 3m of the radius coordinate is characterized by three different properties: (a) there is a ?light sphere,? (b) there is ?centrifugal force reversal,? (c) it is the upper limiting radius for a non-transparent Schwarzschild source to act as a gravitational lens that produces infinitely many images. In this paper we prove a theorem to the effect that these three properties are intimately related in any spherically symmetric static spacetime. We illustrate the general results with some examples including black-hole spacetimes and Morris-Thorne wormholes.
