Origin of the Microwave Background . .

This communication explores an alternative to the conventional interpretation of the cosmic microwave background as the remnant of a primordial fireball. We postulate that the radiation was generated by ordinary astronomical processes (thermonuclear reactions in stars or gravitational collapse of objects of galactic mass) and subsequently thermalized by interaction with dust grains. The observed properties of the radiation (temperature, thermal spectrum, and isotropy) impose severe constraints on any theory of this general character, all of which can be met if most of the matter in the early universe condensed into stars in the mass range 5-10 M0. These stars would have released most of their energy at redshifts 25 <% Z %< 50. Subsequently, during the explosive phase of their evolution, they would have ejected the heavy elements from which the grains required to thermalize the radiation could have formed. The assumption that most of the matter in the universe was once bound in such stars fits naturally into a previously described cosmogonical theory based on the assumption of a zero-temperature initial state. Radiation from collapsing objects of galactic mass could also have contributed to the microwave background, but is unlikely to be the main energy source unless the grains responsible for thermalization were formed from heavy elements created in the initial stages of the expansion and had unusually high radiative efficiency at centimeter wavelengths. The grains responsible for thermalizing the microwave background affect the magnitudes and colors of distant galaxies and quasars. For galaxies with redshifts z < 0.3, the predicted extinctions are small enough to have escaped detection. At larger redshifts, however, the extinction increases steeply with increasing z, reaching 4 mag at z = 3 and 6 mag at z = 4. If the grains have lifetimes of order 10 years, then still larger extinctions at redshifts z 2 would be compatible with the galaxy data. This suggests that the failure to observe quasars with redshifts z > 3 may be due not to a real thinning out of these objects, but to extinction by the grains responsible for thermalizing the microwave background. Subject headings: cosmic background radiation - cosmology - intergalactic medium