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Event horizons and apparent horizons in spherically symmetric geometries

Edward Malec
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Abstract

Spherical configurations that are very massive must be surrounded by apparent horizons. These in turn, when placed outside a collapsing body, must propagate outward with a velocity equal to the velocity of radially outgoing photons. That proves, within the framework of (1+3) formalism and without resorting to the Birkhoff theorem, that apparent horizons coincide with event horizons.

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Edward Malec. 1993-01-06. Event horizons and apparent horizons in spherically symmetric geometries. https://doi.org/10.1103/physrevd.49.6475

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