Planets, stars, asteroids and other celestial bodies have generally round shapes. Some are ovals, others really bumpy circles, and some are a very squished oval. Why are none triangular or rectangular?

Planets revolve and rotate, they go around something and they spin, pretend they are on a road (orbit path) while they rotate and revolve. It's liking rolling a chunk of playdough in your hands to form a ball. same goes for asteroids, stars are auctally gases so that one I'm not sure how to answer.