I've read a little about this already, but I think it would be fascinating for people who never asked...

Can a super-massive black hole get TOO full?

or the other way of asking...

Can a super-massive black hole turn off?

I don't mean that there is nothing left around it to feed it... I mean is there a volume that just won't support the mass anymore and it begins to reject material... or cause negative gravity?

Could they be the source of dark matter?