Interstellar medium

In addition to stars, our galaxy contains abundant diffuse material that is distributed throughout its volume and constitutes what we call the interstellar medium. This medium plays a fundamental role in the life cycle of the stars, since it contains the material to form new generations of stars, and is the resting place of the gas expelled by the stars in their final evolutionary stages.

The interstellar medium is a complex environment. Its material is not uniformly distributed but consists of different phases with temperatures that range from the few degrees above the absolute zero observed in star-forming regions to the millions of degrees typical of supernova remnants. The density of the medium also varies by orders of magnitude with phase, but is always so low that it rivals the densities achieved in the best vacuum chambers of Earth laboratories. Depending on the density and temperature conditions, the interstellar matter can be molecular, atomic, or ionized, although this state is not permanent, since the gas circulates between the different phases following a continuous cycle of galactic evolution.

Due to the very different characteristics of its phases, the interstellar medium needs to be studied using different observational techniques and telescope types. The coldest components of the interstellar medium do not emit visible light, and are observed with telescopes that are sensitive to the weak emission of radio waves that the material produces. Using different radio telescopes, such as the 40 m-diameter one in the Yebes Observatory, those that the Institute for Millimeter Radio Astronomy (IRAM), of which the IGN is a partner, has in Grenoble and Granada, or the Atacama Large Millimeter/submillimeter Array (ALMA) in the Atacama desert of Chile, the astronomers of the Observatorio Astronómico Nacional contribute to characterize the physical and chemical properties of the molecular clouds where stars are born and the circumstellar envelopes produced by stars in the final stages of their lives. The study of these regions is helping us to complete our understanding of the most mysterious phases in the complex cycle of stellar life.