The center of the Milky Way is mysteriously glowing.

Sure, there’s a whole bunch of stars there, along with a black hole 4 million times the mass of the Sun — but subtract the light from all that, and we’re still left with this mysterious excess gamma radiation that suffuses the region.

It’s called the Galactic Center GeV Excess (GCE), and it’s puzzled scientists since its discovery by physicists Lisa Goodenough and Dan Hooper in 2009. In data from NASA’s Fermi telescope, they found excess gamma radiation — some of the most energetic light in the Universe — and we haven’t been able to directly detect whatever is causing it.