The process by which interstellar gas gathers into stars is a fundamental problem in astrophysics, with implications for the formation and evolution of galaxies and the formation of the elements. The structure and evolution of molecular clouds, the sites of Galactic star formation, will be investigated by Dr. McKee. Molecular clouds are observed to be highly clumped, and calculations will determine the nature of the medium between the clumps. The early evolution of a molecular cloud, in which a largely atomic gas becomes molecular, will be calculated. The distribution of pressure in gravitationally bound clumps will be investigated. Calculations will trace the destruction of the clouds by the massive stars that form within them. Shock waves shape the mass spectrum of diffuse interstellar clouds, and powerful hydrodynamic and magnetohydrodynamic computer codes will be used to study the interaction of shocks with clouds. Shock waves can produce water masers, which are signposts of massive star formation, and the conditions under which this can occur will be evaluated. Many of the heavy elements of the interstellar medium, which are produced by stars, are locked up in tiny dust grains; the sputtering, vaporization, and shattering of these grains in interstellar shocks will be calculated.
