Interstellar Medium
The interstellar medium refers to the material—comprised of gas, dust, and cosmic rays—that fills the space between stars within galaxies. It is a crucial component in understanding the life cycle of galaxies, as it serves as both the raw material for star formation and the reservoir that fuels active galactic nuclei. Its physical properties, such as temperature, density, and chemical composition, are shaped by various astrophysical processes, including supernova explosions, stellar winds, and cosmic ray interactions. Studying the interstellar medium is essential to understanding the broader context of cosmic evolution, making it a fitting subcategory under Cosmology in the Science/Space Science hierarchy.