Gravitational instability in a static universe and the angular momentum of galaxies

Abstract

Gravitational instability arising from thermal fluctuations in a static universe in considered in an extrapolation of a weakly non linear approximation, to calculate the mean square angular momentum of proto-galaxies at the critical time at which these protogalaxies detach themselves from the primeval homogeneous medium. The mean angular momentum of a given volume, containing in the mean a mass M, and the mean angular momentum of a given mass M, are shown to be quite different. It is suggested that it is the latter which should be compared with the observed angular momentum of galaxies. A numerical application shows that such a picture cannot account for the observed angular momentum of the Galaxy and at the same time for the existence of dwarf galaxies. A simple calculation suggests however that tidal interactions arising between neighbouring protogalaxies after the critical time of detachment would easily account for the observed angular momentum of spiral galaxies, if these interactions take place before the universe is set in a state of fully developed expansion