  Formation and evolution of general relativistic collapse inhomogeneity is
investigated. It is shown that a rarefaction wave forms at initial collapse
stages and propagates inside from the cloud boundary to its center. The
focusing time of the rarefaction wave is found. In massive clouds, the
rarefaction wave focusing time equals the free-fall time. The collapse of such
clouds leads to black hole formation. In low-mass clouds, the rarefaction wave
focusing time is less than the free-fall time. After focusing, the collapse of
such clouds becomes fully inhomogeneous and can be sufficiently decelerated by
the pressure gradient.
