Thermal radiation of an absolutely black body moving in an equilibrium gas of photons

The dynamics, kinetics of heat transfer and the intensity of thermal radiation of an absolutely black body with its own temperature $T_1$ moving at an arbitrary speed in an equilibrium gas of photons with its own temperature $T_2$ independent of time are considered. Formulas are obtained for the spectral-angular and total radiation intensity, as well as for other quantities in the rest frame of the body and in the frame of reference of the photon gas. It is shown that at the initial moment the radiation intensity of spherical and disk-shaped particles of the same radius depends differently on the speed of motion and the ratio of temperatures $T_1$ and $T_2$. Then a quasi-stationary thermal state of bodies is established with an effective temperature depending on the velocity and temperature $T_2$, the intensity of thermal radiation does not depend on the shape, and the kinetic energy is transformed into radiation. The characteristic time for the establishment of a quasi-stationary state is many orders of magnitude shorter than the characteristic deceleration time.