Accumulation of mass in accelerating self-gravitating gas layers

The two-dimensional motions of a plane layer of self-gravitating gas accelerated by the pressure difference on both sides of the layer have been simulated numerically. The change in the shape of the layer surface has been found to depend significantly on the ratio of gravity and the pressure difference. In the region where the forces of gravitational attraction between the particles of the medium are greater than or of the order of the pressure difference on the layer sides, the structure of the condensations is such that the differences in inhomogeneity scales in the longitudinal and transverse directions with respect to the unperturbed motion decrease significantly compared to the Rayleigh-Taylor instability. Allowance for the self-gravity leads to a considerable increase in the maximum density in the layer. It is shown that the instability of the shell formed during the propagation of the ionization-shock front can be responsible for the emergence of an inhomogeneous structure of the HII region RCW 82, with the instability growth time being less than the estimated age of the HII region.