What is the Interstellar Medium?
The interstellar medium is the gas and dust between stars. Of it’s mass, this gas is composed of mainly hydrogen and helium with a touch of heavier elements. Consisting of atoms and molecules as well as charged particles such as ions and electrons, the ISM is mainly found in two forms.
In cool, dense regions of the ISM, matter is primarily in molecular form with number densities of 106 molecules per cm3. In hotter, more dilute regions of the ISM, matter is ionized, and the density may be as low as 10−4 ions per cm3.
So what’s the significance of the Interstellar medium? Through highly dense regions of the ISM known as molecular clouds, stars are formed. These stars, through planetary nebulae, stellar wind, and supernovae replenish the ISM littering the galaxy with ingredients responsible for the formation of new stars, planets, moons, and life.