Re: Black holes & gravitation / mass acceleration
Hi Matt, welcome to the Forums.
Since this is posted in the Beginners area, I won't go into major details.
First point is that Gravity is not a pulling force, so the answer is "NO" there will not be some massive Black Hole sucking up everything.. including other Black Holes.
The presence of Matter Curves Space_Time. Planets and stuff are not pulled towards a Star, but rather material that comes within a Gravitational field of a Star can be captured into falling into an orbit following the Curvature of Space_Time around that Star.
The Black Hole at the center of a Galaxy is not holding all of it's Stars in that Galaxy together.. but rather each Star is following the Curvature of Space-Time created by the whole Galaxy. Stars are too far apart for their own respective Gravity fields to be barely noticeable by neighboring Stars, let alone something as far away as the center of a Galaxy.
Dark Matter is the key to holding everything together but Science doesn't know what Dark Matter is yet. There are several ideas, but none have been confirmed. All we can say is that Dark Matter re-enforces/amplifies the Curvature of Space-Time and leave it at that.
Since the Universe seems to be inflating at an accelerating pace, then the Big-Crunch is very improbable. Ultimately, every Star will burn out and the Galaxies will cease to give off light. New Stars will cease forming when the raw materials are exhausted. This will leave Galaxies filled with dead Stars having dead planets still orbiting them for a very long time. Some Black Holes may hang around for a very long time as well.. or just evaporate over enough time.
So, the Big Chill is the most likely "End of the Universe" scenario.
Note: My personal favorite is the "Completion Scenario" however. The Universe may cease to Exist when it is "Completed" by it's own definition. That could happen at any minute, long before the Stars die, without any warning. I grant it's a very unlikely ending for the Universe but no one can prove it's impossible. There are several other ideas floating around, just as strange as this one. But it's all pure speculation and we should just stick with what Conventional Science predicts, as I described above before my Note.
Hope that helps,
Ps. I'm just a Science Buff, so perhaps a local Expert may have more to add.