If I still remember from Astronomy class, a nebula is like a star dust cloud that appears when the star dies. I don't know if this applies to the death of big stars as well, since they go super or even hypernova, but they're like the remains of a dead star. It can also gather up until it becomes a new star. Imagine it's like some type of chain. Star death--->Nebula cloud---->Star birth.
[doublepost=1480622469][/doublepost]I think atleast
[doublepost=1480622576][/doublepost]Oh wait the points nvm I'm an idiot.