Аннотация:The features of unstable motions in the regions of active star formation are considered.The purpose of the research is to determine the magnitude and scale of inhomogeneities for which theJeans gravitational compression criterion is satisfied. Mathematical models are used that take intoaccount nonequilibrium radiation processes and self-gravity. The results of calculations of the cumulationof mass during the propagation of the ionization-shock front in the cloud are presented; a qualitativeagreement is established between the motion structure and the one obtained on the basis of thethin layer model Cherny. In the case of Richtmyer–Meshkov instability it was found that density perturbationsincrease significantly due to radiation cooling. Taking into account the gravitational interactionbetween particles of the accelerating moving gas layer, a criterion is formulated for the dominantinfluence of self-gravity on the shape of inhomogeneities compared with the Rayleigh–Taylor instability.Morphologically, heterogeneities of various origins differ little and are observed mainly on theinner side of the ionization-shock front, facing the radiation source. The authors of this work for thefirst time found that gas-dynamic phenomena at the outer boundary of a layer compressed by a shockwave can reflect the presence of condensations that existed in the interstellar medium before the passageof the ionization shock front. Computer modeling has shown that when a condensation (cloud,clot) penetrates into an accelerating moving layer, the formation of a cumulative jet occurs.