Unruh (by definition) effect shows that an accelerating observer will observe black-body radiation. http://en.wikipedia.org/wiki/Unruh_effect It is in a gravitational field. Compton scattering by definition. The inelastic scattering of photons in matter results in a decrease in energy (increase in wavelength) of an X-ray or gamma ray photon, called the Compton effect. Part of the energy of the X/gamma ray is transferred to a scattering electron, which recoils and is ejected from its atom, and the rest of the energy is taken by the scattered, "degraded" photon. http://en.wikipedia.org/wiki/Compton_scattering It is in an EM field. If the the Vacuum (gravitational field) is a plasma of the virtual particle-antiparticle pairs the mechanism of the Unruh and Compton is the same. An accelerating electron in the gravitational field (virtual plasma) absorbs more virtual pairs than emits and does see the thermal bath (the vacuum density increases towards the massive object). An accelerating electron in the EM field absorbs more photons than emits and does see the thermal bath too. http://www.hlawiczes1.webpark.pl/gravastar.html [Broken] Isn't it ?