Dark matter and gamma rays from the galactic halo

The nature of the dark matter in the halo of our Galaxy is still largely unknown. The microlensing events found so far towards the Large Magellanic Cloud suggest that at most about 20% of the halo dark matter is in the form of MACHOs (Massive Astrophysical Compact Halo Objects). The dark matter could also, at least partially, consist of cold molecular clouds (mainly $H_2$). Another possibility is that WIMPs (Weakly Interacting Massive Particles) make up the dark matter and that, due to annihilition processes, they show up through gamma-ray emission.