: The Fermi Gamma-Ray Space Telescope
has detected a halo of gamma rays
extending outward from the center of the Milky Way galaxy. Dan Hooper of Fermilab
and his colleagues believe that the gamma rays are caused by dark matter collisions and claim they have ruled out other possible sources. Further study of their data suggests that the mass of the particles that are colliding is between 30 and 40 GeV. Although that matches simple dark matter models, it is significantly heavier than early measurements of dark matter mass made by direct detection experiments. Observations of gamma-ray emissions from nearby dwarf galaxies, which are expected to have similar halos, or data gathered by the Large Underground Xenon
dark matter experiment may clarify which model is correct.