Jeans instability of interstellar gas clouds in the background of weakly interacting massive particles

Criterion of the Jeans instability of interstellar gas clouds which are gravitationally coupled with weakly interacting massive particles is revisited. It is established that presence of the dark matter always reduces the Jeans length, and in turn, Jeans mass of the interstellar gas clouds. Astrophysical implications of this effect are discussed. Subject headings: dark matter — gravitation — instabilities — ISM: clouds — ISM: kinematics and dynamics — stars: formation Investigation of physical processes in clouds of interstellar gas is important for a number of reasons. There is a strong evidence that the formation of stars occurs through gravitational collapse of the interstellar gas clouds. An important mechanism in triggering the formation of stars and/or stellar clusters is believed to be a high-velocity (supersonic) cloud-cloud collisions in which a dense gaseous slab is formed with two plane-parallel shock fronts propagating away from the interface (Usami et al. 1995). Then the slab grows in mass becoming unstable against gravitational instability which causes its fragmentation. The fragments or the gaseous clumps, in turn, collapse further and evolve into stars and/or stellar clusters. Yet another mechanism for triggering of star formation is Rayleigh-Parker instability which leads to an increase in the curvature of the magnetic field lines that initially were directed parallel to the galactic plane. The interstellar gas clouds move along the field lines (due to the ”frozen in” condition) and fall into the ”wells” of the filed. This causes further stretching of the magnetic field lines, making ”wells” deeper, thus large amounts of gas can fall into the ”wells” creating large concentrations of gas which then becomes gravitationally unstable (Gorbatskii, 1977). In this letter we consider stability of the interstellar gas clouds against Jeans instability in the presence of background weakly interacting massive particles (WIMP). We find that presence of WIMP matter yields an unavoidable reduction of Jeans length, Jeans mass and Jeans time (time-scale of the collapse via Jeans instability). Existence of WIMP matter, one of the possible form of dark matter, the latter itself a dominant mass component of the universe, is strongly motivated both by standard models of particle physics and cosmology. Generally speaking, mass density associated with the luminous matter (stars, hydrogen clouds, x-ray gas in clusters, etc.) cannot account for the observed dynamics on galactic scales and above, (Trimble,