Because everything rotates so perfectly, and we know that some blackholes rotate and they're the biggest things in the universe, so a silly question comes to mind.
If you remove all black holes from a galaxy:
- Would it still rotate?
- Would the rotation of the planets inside it slow down until there's no more rotation/gravity?
I imagine that the black hole has something to do with the fact that we have gravity since it's always rotating and pulling spacetime fabric inward like a tornado. There are 100 million black holes in our galaxy so I think of them as rotation generators.
Last year I read a research paper that the rotation of a black hole can't cause gravity, but forgot why.