You're looking at the best dark matter signal that scientists have ever recorded. Dan Hooper from the Fermi National Laboratory told New Scientist that "this is the most compelling signal we've had for dark matter particles—ever."

The scientists found these extra gamma rays forming a 5,000-light-year sphere around the galactic centre. While some critics suggest the rays could be a result of other celestial bodies—notably a pulsar—Hooper and his colleagues point out that the sphere's size make that unlikely. He explains:
"At this point, there are no known or proposed astrophysical mechanisms or sources that can account for this emission. That doesn't rule out things that no one's thought of yet, but we've tried pretty hard to think of something without success."
The next step, say the researchers, is to spot the same phenomenon with Large Underground Xenon (LUX) detector in South Dakota. [New Scientist]