Density and velocity distribution function for freely expanding matter

Abstract

For a system of noninteracting particles being initially in a spherical volume of a given radius, the density evolution and the distribution function are considered for various initial conditions. In particular, the conditions under which the density during free expansion of a sphere-shaped cloud of noninteracting particles remains spatially constant, while the boundary remains sharp, are determined. Alternative variants of free spherically symmetric expansion of a particle cloud are considered. The results of this consideration are applicable to various problems of the centrosymmetric explosion, and have astrophysical applications.