Hubble flows and gravitational potentials in observable Universe
  In this paper, we consider the Universe deep inside of the cell of
uniformity. At these scales, the Universe is filled with inhomogeneously
distributed discrete structures (galaxies, groups and clusters of galaxies),
which disturb the background Friedmann model. We propose mathematical models
with conformally flat, hyperbolic and spherical spaces. For these models, we
obtain the gravitational potential for an arbitrary number of randomly
distributed inhomogeneities. In the cases of flat and hyperbolic spaces, the
potential is finite at any point, including spatial infinity, and valid for an
arbitrary number of gravitating sources. For both of these models, we
investigate the motion of test masses (e.g., dwarf galaxies) in the vicinity of
one of the inhomogeneities. We show that there is a distance from the
inhomogeneity, at which the cosmological expansion prevails over the
gravitational attraction and where test masses form the Hubble flow. For our
group of galaxies, it happens at a few Mpc and the radius of the
zero-acceleration sphere is of the order of 1 Mpc, which is very close to
observations. Outside of this sphere, the dragging effect of the gravitational
attraction goes very fast to zero.
