Hydrodynamics of galactic dark matter

We consider simple hydrodynamical models of galactic dark matter in which the galactic halo is a self-gravitating and self-interacting gas that dominates the dynamics of the galaxy. Modeling this halo as a sphericaly symmetric and static perfect fluid satisfying the field equations of General Relativity, visible barionic matter can be treated as ``test particles'' in the geometry of this field. We show that the assumption of an empirical ``universal rotation curve'' that fits a wide variety of galaxies is compatible, under suitable approximations, with state variables characteristic of a non-relativistic Maxwell-Boltzmann gas that becomes an isothermal sphere in the Newtonian limit. Consistency criteria of the model leads to a minimal bound for particle masses in the range 30-60 eV, while a constraint between the central teperature and the particles mass suggests acceptable mass values on the range between 0.5 and 100 keV, a figure that coincides with current mass estimates of self-interactive CDM and WDM structure formation theories.