BISTABILITY IN DARK CLOUD CHEMISTRY

In this Letter we present the first report of a double steady state chemical solution in dark interstellar clouds. The discussion focuses on examples such as the degree of ionization and the C/CO ratio, but all the chemical abundances are concerned. The role of density and temperature is considered, and we explore the relevant range of these parameters where bistability occurs under interstellar conditions. The results are then discussed in terms of time evolution toward the two steady state solutions which are referred to as a low- and a high-ionization phase (LIP and HIP). We point out that the nonlinear interstellar chemical equations have the intrinsic property of bistability. Some possible implications of this new approach to the interstellar medium are outlined.