How do gravitationally collapsing gases create stars and planets?
Suppose you start with a uniform cloud of gas. It will stay a cloud of gas. But then suppose some little spot happens to become a little bit concentrated – then the higher density spot will attract more matter to it. It will then get denser, and attract yet more matter, and so on; eventually you will get a high density clump of stuff. A sufficiently high mass clump will contract, heat up, and ignite nuclear fusion- and a star is born. Planets are thought to grow from clumps in dust and gas clouds surrounding newly-born stars. We’ll talk much more about these topics later.
