are black holes just dead stars with lots of mass which shrunk to small size and got lots of gravity, or an actual hole in space-time? if they're actually holes, where do they lead stuff that gets in them? if they're just dead stars with lots of gravity, their mass must grow over time because of all the dust and stars they attract, right? now, about gravity, why do stars with lower gravity just circle around other stars with bigger gravity instead of colliding into each other? if they're attracted to each other because of gravity, what's keeping them apart so they don't collide?