Thermal radiation of various gravitational backgrounds

We present a simple and general procedure for calculating the thermal radiation coming from any stationary metric. The physical picture is that the radiation arises as the quasiclassical tunneling of particles through a gravitational barrier. We study three cases in detail: the linear accelerating observer (Unruh radiation), the nonrotating black hole (Hawking radiation), and the rotating/orbiting observer (circular Unruh radiation). For the linear accelerating observer we obtain a thermal spectrum with the usual Unruh temperature. For the nonrotating black hole we obtain a thermal spectrum, but with a temperature twice that given by the original Hawking calculations. We discuss possible reasons for the discrepancies in temperatures as given by the two different methods. For the rotating/orbiting case the quasiclassical tunneling approach indicates that there is no thermal radiation. This result for the rotating/orbiting case has experimental implications for the experimental detection of this effect via the polarization of particles in storage rings.