  A new model for the postcollapse equilibrium structure of virialized objects
which condense out of the cosmological background universe is described and
compared with observations and simulations of cosmological halos from dwarf
galaxies to X-ray clusters. The model is based upon the assumption that
virialized halos are isothermal, which leads to a prediction of a unique
nonsingular isothermal sphere for the equilibrium structure, with a core radius
which is approximately 1/30 times the size and a core density which is
proportional to the mean background density at the epoch of collapse. These
predicted nonsingular isothermal spheres are in good agreement with the
observations of the internal structure of dark-matter-dominated halos from
dwarf galaxies to X-ray clusters.
