Interstellar medium

matter and radiation in the space between the star systems in a galaxy

In astronomy, the interstellar medium (sometimes called the ISM) is the mix of plasma, gas, and dust in outer space between the stars of a galaxy. It is made mostly of ions, atoms, molecules, cosmic dust, and cosmic rays.

Eagle nebula. Pillars made of dense cold gas are visible.

Various gases exist in outer space. Most common are hydrogen and helium. Interstellar cosmic dust makes nebulae.