The Energy Spectrum of Radiation in the Expanding Universe

Abstract

A combination of theoretical arguments and observational evidence suggests the existence of a moder-ately hot, fully ionized intergalactic gas. In the process of heating this gas, distortions of the residual black-body radiation could arise. (This black-body radiation has been detected by several workers and seems to have a temperature of about 3° K.) This possibility is investigated by integrating the differential equations describing the evolution of the radiation field subject to interaction with a hot gas by Compton-scattering, bound-free, and free-free processes. It is suggested that, in addition to the X-ray emission produced by a hot gas, it would be useful to attempt to find distortions of the black-body-curve around 300 p and 30 cm. Failure to find such distortions would exclude the possibility that the gas was heated at very early epochs in the expansion.