Limits? What Limits?
How would an advanced galactic empire generate its power?
Some fraction of the radiation seething from the disk would be reflected and focused onto the power plants. Each power plant would transmit collected energy as a collimated microwave beam from a 100-mile diameter antenna. _Discovery
A truly advanced civilisation on the Kardashev scale would harness the power of black holes to drive starships (PDF), power their industries, and gain control over both matter and time. We may have a few years to go before reaching that level.
A consortium of super-civilizations might pool resources to build a chain of power stations encircling the black hole. It would be the heart of a robust and fault-tolerant energy grid connecting numerous worlds like a fantasy scene out of the film "Tron."
However, I think it is more likely that a federation of expanding space colonies, spawned from a single mother civilization, would work together to maintain their viability. This wouldn't run into the thorny question of how two or more independent but similarly co-evolved species manage to contact each other and work out a practical energy infrastructure. _Discovery
Researchers at the U.S. Department of Energy's Los Alamos National Laboratory believe that magnetic field lines extending a few million light years from galaxies into space may be the result of incredibly efficient energy-producing dynamos within black holes that are somewhat analogous to an electric motor....The energy in these huge magnetic fields is comparable to that released into space as light, X-rays and gamma rays. In other words, the black hole energy is being efficiently converted into magnetic fields.
Colgate and Los Alamos colleagues Vladimir Pariev and John Finn have developed a model to perhaps explain what is happening. They believe that the naturally magnetized accretion disk rotating around a black hole is punctured by clouds of stars in the vicinity of the black hole, like bullet holes in a flywheel. This, in turn, leads nonlinearly to a system similar to an electric generator that gives rise to a rotating, but invisible magnetic helix.
In this way, huge amounts of energy are carried out and away from the center of a galaxy as a set of twisted magnetic field lines that eventually appear via radio waves from luminous cloud formations on opposite sides of the galaxy. _SD
So you see, humans do not yet understand how black hole energy is converted into all the forms of energy that are propagated within and throughout the galaxy. But give us some time -- and a respite from all the energy starvationists hounding our steps -- and we just might take it to the next level.
Cross-posted from Al Fin blog