A little over one year ago I figured out how gravity works: Imagine a particle. Now open up the particle and get all the stuff out of it and close it back up. What's inside? It's not matter, so it has nothing inside with a huge vacuum. (Anti-matter is another way of saying "nothing".) That's gravity on the small scale like a hydrogen atom.
Now, imagine the sun with some iron in it. Iron boils and creates a big bubble of iron. That's the core of the earth; filled with nothing. Iron is a ferrous material like a sponge.