ISM (Interstellar Medium)

The interstellar medium (ISM) is the matter and energy that exists in the space between stars within a galaxy. It consists mainly of gas—primarily hydrogen and helium—along with dust particles and cosmic rays. Though it may seem empty, the ISM plays a crucial role in astronomical processes, such as star formation, by providing the raw materials that create new stars and planets. The conditions within the ISM vary widely, with some regions being very dense and others very diffuse, influencing how stars and other celestial objects evolve.