Interaction of Hawking radiation with static atoms outside a Schwarzschild black hole

Abstract

We study the spontaneous excitation of static two-level atoms interacting with Hawking radiation of a massless scalar field in the Hartle–Hawking vacuum outside a four-dimensional Schwarzschild black hole, and calculated the contributions of the vacuum fluctuations and radiation reaction to the rate of change of the mean atomic energy. We show that an atom held static outside the Schwarzschild black hole spontaneously excites as if it were in a thermal bath of radiation at a proper temperature which reduces to the temperature of Hawking radiation in the spatial asymptotic region. Our discussion, therefore, establishes an interesting relationship between the existence of Hawking radiation and the spontaneous excitation of a static two-level atom in vacuum in the exterior of a black hole.