So what produces gamma-rays in large numbers? The first thing that comes to mind is a gamma-ray burst, produced when a massive star dies and collapses as a supernova. But this is short-lived and not sustained. How about the supermassive black hole sitting in the middle of the Milky Way’s galactic nucleus? This theory was recently discussed on Astroengine, but the production of antimatter (i.e. positrons) is more of a slow leak than anything substantial, certainly not of the scale that is being measured. As we are dealing with gamma-rays of the exact rest mass energy as a positron, so we know that the source is some kind of positron annihillation. What could possibly be doing this?