The picture on the left is a raw image of the x-rays detected by the Fermi Gamma-ray Space Telescope looking toward the center of the galaxy. The image on the right is same data with the known sources subtracted. Where are the excess x-rays coming from?
One controversial hypothesis that seems to explain the data involves a type of dark matter known as WIMPs colliding with themselves to create the detected gamma-rays. Finding the nature of dark matter is one of the great quests of modern science, and this type of cosmologically pervasive matter has shown itself thus far only through gravitation.
Image Credit: NASA