Plasma Physics Processes of the Interstellar Medium

This “white paper” is directed to the GAN (galactic neighborhood) theme of the Decadal Survey. We are particularly interested in interstellar medium (ISM) phenomena which can be described by the laws of plasma physics. This is appropriate since nearly all of the ISM phases possess sufficient ionization for plasma behavior. Our advocacy of this position comes from the conviction that many of the important processes and phenomena which occur in the ISM may elude satisfactory understanding until the plasma physics aspects are recognized, and results and methods of plasma physics brought to bear on them. Study of the interstellar medium is a major disciplinary area of astronomy and astrophysics. It is here where the process of star formation occurs. The cosmic rays are probably accelerated in the ISM, and its properties certainly govern their propagation and diffusion. In the rest of this document, we identify some of the most interesting and important topics in the astrophysics of the interstellar medium, which merit attention by the astronomy community in the next decade. The theme of this white paper was chosen by the Topical Group on Plasma Astrophysics of the American Physical Society.