Publication date: Aug 2013
Abstract:
The study of the statistical properties of collisionless systems formed
by neutral particles subject to gravitational field represents an
intriguing theoretical issue. In astrophysics, it directly relates to
the description of collisionless gravitating dark matter (DM) halos.
Structures of this type are expected to be characterized by
intrinsically non-Maxwellian kinetic distribution functions (KDFs) and
to exhibit temperature anisotropy, i.e. an anisotropy in the directional
particle velocity dispersions. In this paper, a theoretical analysis of
the issue is proposed, based on the kinetic theory developed in the
framework of the Vlasov-Poisson description for nonrelativistic DM
systems at equilibrium. By implementing the method of invariants,
explicit solutions for the equilibrium KDFs are constructed and
expressed through generalized Gaussian distributions. A perturbative
theory is developed which allows them to be cast in terms of
Chapman-Enskog series representations and to evaluate analytically the
corresponding fluid fields. The conditions for the occurrence of
temperature anisotropy are investigated for different physical and
geometrical configurations. It is shown that this feature can arise at
equilibrium due to specifically-kinetic effects associated with
phase-space conservation laws in the presence of a nonuniform
gravitational field.
Authors:
Cremaschini, Claudio; Stuchlík, Zdeněk;