tonyshowoff
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No, they aren't. Nebulae originally were any object that didn't seem to be a planet or star, especially if it was cloudy looking. For example, Andromeda was originally classified as a nebula, but with better optics, we now know it's a galaxy heading right for us. The term nebula though has stayed in use for the large clouds where stars are "born."
Not all stars create black holes at the end of their lives, and super massive black holes were not created by collapsing stars but instead were created shortly after the creation of the universe. Black holes aren't a rift in space, they're just so dense that not even light can escape their clutches.
As for the last part, proto-planetary disks around stars often coalesce into planets, yes, but stars don't exist to hold planets in place anymore than the the Earth exists so that you have something to stand on.
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