Entropy changes in the clustering of galaxies in an expanding universe

Abstract

In the present work the approach-thermody-namics and statistical mechanics of gravitating systems is applied to study the entropy changein gravitational clustering of galaxies in an ex-panding universe. We derive analytically the expressions for gravitational entropy in terms of temperature T and average density n of the par-ticles (galaxies) in the given phase space cell. It is found that during the initial stage of cluster-ing of galaxies, the entropy decreases and finally seems to be increasing when the system attains virial equilibrium. The entropy changes are studied for different range of measuring correlation parameter b. We attempt to provide a clearer account of this phenomena. The entropy esults for a system consisting of extended mass (non-point mass) particles show a imilar behaviour with that of point mass particles clustering gravitationally in an expanding uni-verse.