DETECTABILITY OF GAMMA-RAYS FROM CLUMPS OF DARK MATTER

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), γ-rays produced by their annihilation would in principle be observable1,2. But the expected flux3 from a smoothly distributed dark matter halo4,5 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 matter1,3. 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 spectrum2,3 and a line feature in sufficiently bright sources3,7. Even Geminga9,10, the second strongest source of γ-rays at energies greater than 50 MeV, could be annihilating dark matter. © 1990 Nature Publishing Group.