Here's a breakdown:

* Interstellar Medium: The space between stars isn't empty. It's filled with a mixture of gases, primarily hydrogen and helium, along with dust and other elements. This is called the interstellar medium.

* Molecular Clouds: These are dense regions within the interstellar medium, rich in molecules like carbon monoxide, water, and ammonia. These clouds are the birthplace of stars.

* Supernova Remnants: When massive stars die in supernova explosions, they release enormous amounts of gas and heavy elements into space, enriching the interstellar medium.

So, the Milky Way is far from a vacuum. It's a dynamic environment where gases play a crucial role in star formation, galaxy evolution, and the overall composition of the universe.