On the Dissipation of Primordial Turbulence in the Expanding Universe

The growth of primordial density contrasts and their separation from the general expansion of the universe are the first step in the course of galaxy formation, which has been attempted to describe by various mechanisms. The epoch of the separation depends on the amount of density contrasts at some epoch, which must be more than several billion years ago. In the case of ~ravitational instability there arises some lower limit for the initial density contrast which cannot be explained by the statistical origin.> It has been expected, on the other hand, that thermal instability may play an important role at an early stage of the growing of the density contrasts.),S) This mechanism can be effective, only if heating and cooling balance each other so as to keep matter at high temperature (at least higher than 10 °K) at the pregalactic stage. However, if no heating source of matter exists, the matter temperature Tm downs faster than the radiation temperature Tr after the epoch of the decoupling at Tr4000°K. > The rotational and peculiar motions of the galaxies in the present state suggest us a possibility that enormous turbulent motions have existed at the pregalactic stage. Weizsacker> and Gamow> insisted upon its importance in the problem of galaxy formation. To meet with this, the theory of turbulence in the expanding universe has been developed by one of the authors (H. N.).>•*> On the basis of a more realistic picture for the hot universe motivated by the discovery of cosmic black-body radiation, Ozernoi and Chernin> have recently