Question: the sun keeps the solar system but what keeps the sun up.

Daniel Williams answered on 13 Nov 2017:

The sun is held together by its own gravity; it has enough stuff in it that gravity holds it together, just like the planets have enough gravity to hold themselves together.

While planets orbit the Sun, the Sun doesn’t orbit a single object in the same way. It orbits around the centre of the Galaxy, which is made up of billions of stars. We think that at the very centre there is a supermassive (really big) black hole which helps to hold everything together.