Gravitational wave emission from the CMB and other thermal fields

We calculate the gravitational wave power density emitted by quantum thermal sources. As particular cases, we calculate the emission of gravitational waves from the cosmic microwave background and from stellar sources. We study how treating gravity classically affects the prediction of the thermal emission. We find that the predicted emitted gravitational wave radiation does not exhibit an ultraviolet divergence, even if gravity is treated classically, as long as the fields describing the thermal source are quantum mechanical.