BARYONIC DARK CLUSTERS IN GALACTIC HALOS

Besides MACHOs (Massive Astrophysical Compact Halo Objects) discovered by microlensing, cold molecular clouds (mainly of H-2) may well contr ibute substantially to the galactic halo dark matter. We describe a mo del for the formation and evolution of proto globular clusters towards either globular clusters or dark clusters of MACHOs and molecular clo uds, depending on the distance from the galactic centre. Moreover, we discuss various methods to test this scenario, which rely upon observa tions in several bands of the electromagnetic spectrum. In particular, we estimate the gamma-ray flux arising from halo molecular clouds thr ough the interaction with high-energy cosmic-ray protons. Molecular cl ouds can also be detected via the absorption lines they would produce in the spectrum of stars located in the Large Magellanic Cloud and via the anisotropy they would introduce in the Cosmic Background Radiatio n when looking at the halo of M31 galaxy. Finally, we address the poss ibility of discovering MACHOs by infrared searches.