1. Department of Astronomy, FM-20, University of Washington, Seattle, Washington 98195, USA

Abstract

IF the dark matter in our Galaxy is made up of weakly interacting massive particles (WIMPs) with masses of the order of several GeV (for example, photinos or Higgsinos), -rays produced by their annihilation would in principle be observable^1,2. But the expected flux³ from a smoothly distributed dark matter halo^4,5 is much smaller than the observed diffuse background⁶, and although narrow lines might be produced, their intensity would be much too low to see with the Gamma Ray Observatory (GRO)^3,7. A complementary approach is to consider unique spatial signatures. Numerical simulations of galaxy formation⁸ show that even in the central bulge of the Galaxy, the mean density of the dark matter could be equal to that of the stars. If this were so, GRO could see the Galactic Centre as a source of annihilating dark matter^1,3. Other lumps formed as part of the hierarchical formation of the Galaxy could also produce sources that would be recognized by the shape of their continuum spectrum^2,3 and a line feature in sufficiently bright sources^3,7. Even Geminga^9,10, the second strongest source of -rays at energies greater than 50 MeV, could be annihilating dark matter.