A team of astrophysicists at the University of California San Diego (UCSD) has solved a mystery that led some scientists to speculate that the distribution of certain gamma rays in our Milky Way galaxy was evidence of a form of undetectable “dark matter” believed to make up much of the mass of the universe. Rather, the random gamma rays can be explained by the ejection of “antimatter positrons” from supernovae and the radioactive decay of elements. When an electron and positron encounter each other in space, the two particles annihilate each other and their energy is released as gamma rays.