What in the Space Between Stars?

We often think of space as the absence of matter, but actual space is not really all that empty. The stars and planets are scattered throughout the galaxies, and between them is a vacuum filled with gas and dust. The gases between galaxies are often there due to a galaxy collision that rips gases away from each of the galaxies in involved. In addition, if conditions are right, supernova explosions can also drive hot gases out into intergalactic space.