“Two recent studies by teams in the U.S. and the Netherlands have shown that the gamma-ray excess at the galactic center is speckled, not smooth as we would expect for a dark matter signal. Those results suggest the speckles may be due to point sources that we can’t see as individual sources…” -Eric Charles
When NASA’s Fermi satellite began operations, it didn’t take long before we had constructed the most accurate, comprehensive gamma ray map of the galaxy. While many outstanding astrophysics findings ensued, including the discovery of many new pulsars, there was one particular mystery that came about as well: an unexplained excess of gamma rays from the galactic center. Many possible explanations emerged, but one gathered a disproportionately large and exciting amount of attention: that of dark matter annihilations.
In some models of dark matter, it’s a particle that’s its own antiparticle. If dark matter/dark matter annihilation occurs, it could produce excessive gamma rays, as well as cascades of new particle/antiparticle pairs that would result in a photon signal peaked at 511 keV, as positrons annihilated with electrons. After a huge effort to uncover the nature of this gamma ray excess, Fermi finally has an answer.