In the Beginning, there was a proton and an electron. They combined to form, hydrogen. They lived in an enormous cloud with many other hydrogen atoms.

Other atoms are found, too:

27% Helium, and trace amounts of C, O, N, Fe, Mg, Si, etc..

This is a COOL NEUTRAL HYDROGEN CLOUD

They have typical densities of just ONE atom (usually hydrogen) per cm³!

But, sometimes.. one atom gets a bit too close to another. This means the gravitational pull is just a bit greater between them, and they begin to pull towards each other. Soon, their mutual gravity attracts still more atoms..

The density grows.