The molecular universe

Abstract

This chapter presents a description of the interstellar medium. It starts with a summary of the interstellar medium structure and how the various phases are related to each other. The emphasis is put on molecular clouds, and on their densest regions, the dense cores, which are the birth place of stars. The evolution of matter during the star formation process and its observable consequences, especially in term of chemical composition is presented. The next section is dedicated to the constituents of the interstellar medium, with separate presentations of the gas species and the dust grains. Methods used by astronomers to derive useful information on the structure, temperature, ionization rate of interstellar environments as well as magnetic fields are briefly described. The last part of the chapter presents the telescopes and their instruments used for studying the interstellar medium across the electromagnetic spectrum.