The ingoing Vaidya metric describes a spherically symmetric spacetime sourced by radial null matter, using advanced time and areal radius . In geometrized units it is . A constant mass function reduces it to the Schwarzschild metric in ingoing null coordinates; a varying mass function changes the curvature and the radial null geodesics.
The Vaidya metric is a solution to the Einstein field equations in general relativity that describes the spacetime geometry around a radiating body. It is particularly useful for modeling scenarios where a star or another massive object is losing mass due to radiation, which can occur during supernovae, for example. The Vaidya solution is an extension of the Schwarzschild solution, which describes the gravitational field outside a non-radiating, spherically symmetric massive body.
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