  Propagation of strong shock wave in the expanding universe is studied using
approximate analytic, and exact numerical solution of self-similar equations.
Both solutions have similar properties, which change qualitatively, depending
on the adiabatic powers $\gamma$. In the interval $1<\gamma<\gamma_{cr} \sim
1.16$ analytic and numeric solutions fill all the space without any voids and
they are rather close to each other. At larger $\gamma>\gamma_{cr}$ a pressure
becomes zero at finite radius, and a spherical void appears around the origin
in both solutions. All matter is collected in thin layer behind the shock wave
front. The structure of this layer qualitatively depends on $\gamma$. At the
inner edge of the layer the pressure is always zero, but the density on this
edge is jumping from zero to infinity at $\gamma \approx 1.4$ in both
solutions.
