Physical Processes in the Interstellar Medium
  Interstellar space is filled with a dilute mixture of charged particles,
atoms, molecules and dust grains, called the interstellar medium (ISM).
Understanding its physical properties and dynamical behavior is of pivotal
importance to many areas of astronomy and astrophysics. Galaxy formation and
evolution, the formation of stars, cosmic nucleosynthesis, the origin of large
complex, prebiotic molecules and the abundance, structure and growth of dust
grains which constitute the fundamental building blocks of planets, all these
processes are intimately coupled to the physics of the interstellar medium.
However, despite its importance, its structure and evolution is still not fully
understood. Observations reveal that the interstellar medium is highly
turbulent, consists of different chemical phases, and is characterized by
complex structure on all resolvable spatial and temporal scales. Our current
numerical and theoretical models describe it as a strongly coupled system that
is far from equilibrium and where the different components are intricately
linked together by complex feedback loops. Describing the interstellar medium
is truly a multi-scale and multi-physics problem. In these lecture notes we
introduce the microphysics necessary to better understand the interstellar
medium. We review the relations between large-scale and small-scale dynamics,
we consider turbulence as one of the key drivers of galactic evolution, and we
review the physical processes that lead to the formation of dense molecular
clouds and that govern stellar birth in their interior.
