Page 5, Stars, Formation & Structure: [Previous Page] [Next Page] [Class Home Page] Text Pages 269-270

To understand stars, we must start at the beginning..

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. As the density of the gas grows, molecules can even form. These are called MOLECULAR CLOUDS

Also, microscopic pieces of dust exist in the interstellar medium. Typically just 1% of the mass in the interstellar medium is attributable to such small particles.