Violent relaxation and mixing in non-uniform one-dimensional gravitational systems

Abstract

A series of numerical experiments on non-uniform one-dimensional gravitational systems have been performed with the aim of testing the conflicting models of violent relaxation, developed by Lynden-Bell and by Shu. It is shown that the phase fluid model of Lynden-Bell ceases to apply to the particle systems investigated already at the end of the virialisation phase. From then on the particle nature of the system dominates its evolution: a very efficient mixing process, driven by the mean field fluctuations, washes out all memory of the initial phase densities. During this collisionless mixing process and in the absence of formation of structure, the system evolves towards a configuration characterized by a single temperature per unit mass in accordance with the Shu model of violent relaxation.