Have they considered a Black Hole which has already consumed all that was within it's gravitational pull?
Really not likely. Just because something is a black hole doesn't give it the ability to reach out and grab stuff from VERY far away. It's just that a black hole is a super dense source of gravity. If our sun turned into a black hole(other than the obvious lack of energy we get from the sun), nothing would change for us, it's just that the volume of the sun would decrease as all the matter got collapsed into a smaller volume. The Earth would still orbit our "black hole sun" as before. The size of a black hole that would "eat" an entire galaxy, like what you suppose, would be enormous. The best estimate is that the black hole at the center of our galaxy has the mass of 2-3 million suns(astronomers use our's as the messuring block). And we are no in danger of getting sucked into the center of our galaxy.
I don't understand what's involved, that's for sure! The article says they studied the distribution of hydrogen atoms . . . So my guess is they've seen a giant swirling cloud of hydrogen atoms, but no stars, and not enough hydrogen mass to hold it all together, and so spread out and gigantic it can't be a black hole. Total guess.
"Have they considered a Black Hole which has already consumed all that was within it's gravitational pull?"
No, it's probably not that. They know where Hillary is at all times. ;)