  Gravitating bodies in motion, regardless of their constitution, always
produce electromagnetic radiation in the form of photon pairs. This phenomenon
is an analog of the radiation caused by the motion of dielectric (or magnetic)
bodies. It is a member of a wide class of phenomena named dynamical Casimir
effects, and it may be viewed as the squeezing of the electromagnetic vacuum.
Production of photon pairs is a purely quantum-mechanical effect.
Unfortunately, as we show, the emitted radiation is extremely weak as compared
to radiation produced by other mechanisms.
