Heat- and radiative-driven implosion of interstellar clouds. i. initial dynamics

Abstract

Abstract The hydrodynamics of a spherical cloud, surrounded by hot intercloud gas or exposed by heating radiation, is investigated. Two principal types of hydrodynamical flows are shown to exist simultaneously: an outflow of gas from the outer layer of the cloud that corresponds to the cloud's evaporation, and cumulative compression of the cloud's interior. The cause of such flows is a pressure excess in the outer layers of the cloud created by heating of the cloud's gas by thermal conductivity or by radiation, which is assumed to be absorbed by the surface layers. The qualitative features of the dynamics of evaporating and compressing gas are described. In particular, an amplifying of the magnitude of compression of the cloud's interior in models with a dominating role of electronic conductivity and volume cooling is shown. The importance of these effects for the physics of interstellar matter is discussed.