On the Hawking radiation associated with an Oppenheimer-Snyder collapsing star

Abstract

The author discusses on the basis of the geometrical optics approximation the development of the Hawking radiation in the spacetime of a black hole resulting from an Oppenheimer-Snyder collapsing star. To the extent that he can use this approximation it is shown that the asymptotic flow of radiation to future null infinity does not depend on the specific parameter describing the initial condition for the stellar collapse (in his model the initial radius). Further, at a large distance from the black hole a definition of the radial part of the radiation is given via the concept of normal ordering of the energy-momentum tensor operator with respect to a 'local ground state' of the Schwarzschild metric. It is shown that the ambiguity in this definition which results from the existence of many possible local ground states does not affect the radial part, but enters only in other parts of the radiation.