DENSITY PERTURBATIONS IN A COSMOLOGICAL DE DONDER GAUGE

Density perturbations are considered during the radiation-dominated an d the dust-dominated periods of the expanding universe. The perturbati ons are taken to have spherical symmetry and the investigation is carr ied out in the de Donder gauge. In order to guarantee the energy momen tum conservation of the perturbation in the de Donder gauge a compatib ility condition is obtained. Equations for the propagation of a spheri cally symmetric perturbation in linear approximation on a FRW cosmolog ical background are presented. It turns out that the evolution tendenc y of the formation is mainly predicted by the state of the cosmic back ground. A radiation-dominated universe does not stimulate growth proce sses; the perturbation will be in a frozen state or it will diffuse. I t is found that the dust-dominated universe stimulates the perturbatio n mass to grow. The rate of this cosmic affected growing process is pr oportional to R(-1) (R being the scale factor of the universe), so tha t it seems that almost all galaxies were formed at the beginning of th e present dust-dominated era.