I was doing some reading on X-ray binaries and got to reading the wikipedia article on it: http://en.wikipedia.org/wiki/X-ray_binary When I read this line: "The infalling matter releases gravitational potential energy, up to several tenths of its rest mass, as X-rays. (Hydrogen fusion releases only about 0.7 percent of rest mass.)", a question popped into my mind. Where does the energy potential in gravitational potential energy come from? If energy is conserved, then when the black hole forms is that energy just coming from the gravitational potential of every particle within the the black hole with every other particle in the universe? In that case it would take the equivalent of the released energies of the gravitational potential energy, in such a case as an x-ray binary, to return things as they were. If that's the case then why is the universe not collapsing in on itself - where does the energy come from that drives that drives a continual increase in gravitational potential energy. Is it just the kinetic energy of all bodies moving outwards from the center of the universe? Does this mean that the kinetic energy is continually converted and will eventually run out (the answer is obviously more complex than this since the universe is said to be expanding)?