Solar systems and black holes.
A lot of solar systems are very different than ours. In the beggining of each solor system has hundreds of planets and rocks crashing into each other and ruining each other. It is survival of the strongest and fittest planets.
When people hear the word black hole, it usually associates with fear and wonder. I know that I am very scared of black holes, but they are so interesting to me. Black holes are very messy when they swallow objects, spitting gas every where. When something enters a black hole, we see it like it hasn't moved, but in reality it has already been sucked up. But black holes aren't all bad! They help create galaxies. Black holes are created by Hyper Novas or gigantic stars when they explode. The center of our galaxy is a black hole. But we cannot see black holes. Ponder that for a while.