BINARY BROWN DWARFS IN THE GALACTIC HALO

Microlensing events towards the Large Magellanic Cloud imply that a si zeable fraction of dark matter is in the form of MACHOs (Massive Astro physical Compact Halo Objects), presumably located in the halo of the Galaxy. Within the present uncertainties, brown dwarfs are viable cand idates for MACHOs, Various considerations strongly suggest that a larg e number of MACHOs should actually consist of binary brown dwarfs, Yet this circumstance appears to be in flat contradiction with the fact t hat MACHOs have been detected as unresolved objects so far, We show th at such an apparent paradox does not exist within a model in which MAC HOs are clumped into dark clusters along with cold molecular clouds, s ince dynamical friction on these clouds makes binary brown dwarfs very close. Moreover, we argue that future microlensing experiments with m ore accurate photometric observations can resolve binary brown dwarfs.