Astrophysical limits on massive dark matter

Annihilations of weakly interacting dark matter particles provide an import ant signature for the possibility of indirect detection of dark matter in g alaxy haloes. These self-annihilations can be greatly enhanced in the vicin ity of a massive black hole. We show that the massive black hole present at the centre of our galaxy accretes dark matter particles, creating a region of very high particle density. Consequently the annihilation rate is consi derably increased, with a large number of e(+)e(-) pairs being produced eit her directly or by successive decays of mesons. We evaluate the synchrotron emission (and self-absorption) associated with the propagation of these pa rticles through the galactic magnetic field, and are able to constrain the allowed values of masses and cross sections of dark matter particles.