Physical processes in the interstellar medium

This book deals with the nature of interstellar matter, treating both the rarefied hydrogen and helium gas pervading the universe and the heavier atoms present in both the gas and dust grains. Observational results on all phases of the interstellar medium are summarized, various local phenomena occurring in the gas and in dust grains are discussed, and elastic collisions are studied in detail. Those interactions of the gas with radiation that can be understood without any detailed analysis of excitation conditions are examined and then treated on the basis of the steady-state equation, which is also used to analyze ionization, dissociation, and gas heating. The optical properties of grains and corresponding results for grain radii, composition, and mean density are presented; results of optical polarization studies and an alignment analysis are also reported. The theory of such grain properties as electric charge, temperature, radiative acceleration, and likely evolution is considered. The overall equilibrium and dynamics of the interstellar gas are investigated, including explosions of H II regions and supernova shells as well as processes of star formation.