Cosmic turbulence and the origin of galaxies

It is shown that, contrary to previous assertions, turbulence in the Universe cannot be supported against viscous decay after the epoch teq when the energy densities of matter and radiation are equal. Indeed, the decay is so rapid that for cosmological models with density parameter h2 > h2 = 0.06 the turbulent eddies cannot develop large density variations after the epoch of recombination. This value of h2 is determined by making rather conservative estimates for the rate of decay of the turbulence, and it is not unlikely that future developments will lower its value still further. The problem of galaxy formation in cosmological models with h2 < is also considered. It is shown there that a satisfactory picture for the origin of spiral galaxies can be produced, but only if the process of condensation of material into galaxies is very efficient. The theory has difficulty in accounting for the origin of the elliptical galaxies if these are systems of low specific angular momentum. An alternative theory of galaxy formation, based on the dissipation of strong turbulence of , is presented. In this theory, galaxies form from density perturbations which are developed at teq as a result of the decay of turbulence, and the problems of the turbulence theories are thereby avoided. The theory has only one arbitrary parameter, h2 (which is at least one less than in other theories of galaxy formation presented so far), and for agreement with observation, Qh2 0.25. With this value, it is possible to explain the typical masses and angular momenta of large galaxies, and also their present mean densities. Subject headings: cosmology - galaxies - turbulence