PHYSICAL CAUSES OF ENERGY DENSITY INHOMOGENIZATION AND STABILITY OF ENERGY DENSITY HOMOGENEITY IN RELATIVISTIC SELF-GRAVITATING FLUIDS

We identify the factors responsible for the appearance of energy density inhomogeneities in a self-gravitating fluid, and describe the evolution of those factors from an initially homogeneous distribution. It is shown that a specific combination of the Weyl tensor and/or local anisotropy of pressure and/or dissipative fluxes entails the formation of energy density inhomogeneities. Different cases are analyzed in detail and in the particular case of dissipative fluids, the role of relaxational processes as well as nonlocal effects are brought out.