The Energy Output of the Universe
  The total energy emitted by the growth of massive black holes is large and can be 10-50 per cent of that emitted by stars in the universe. I show how the X-ray Background provides a good measure of this energy and also why most accretion power is absorbed and re-emitted in the far infrared band. A model for the obscured growth of massive black holes is presented which accounts for both the high absorption and the observed black hole to galaxy spheroid mass correlation. Future missions should detect the obscured X-ray sources associated with the growth of massive black holes. 
A. C. Fabian (Institute of Astronomy, University of Cambridge)