  We analyze the gravitational radiation emitted from a particle in circular
motion around a Schwarzschild black hole using the framework of quantum field
theory in curved spacetime at tree level. The gravitational perturbations are
written in a gauge-invariant formalism for spherically symmetric spacetimes. We
discuss the results, comparing them to the radiation emitted by a particle when
it is assumed to be orbiting a massive object due to a Newtonian force in flat
spacetime.
