Dark clusters in galactic halos?

It is proposed that the invisible mass in galactic halos may consist of one million solar masses dark clusters. Such clusters would be able to heat the stellar disks in galaxies, just as in the Lacey and Ostriker (1985) supermassive black hole scenario, but dynamical friction would not necessarily drag too many of them into the galactic nucleus and would avoid accretion of interstellar gas, making them excessively luminous as they traverse the disk. The dynamical friction problem can be circumvented because the clusters may be disrupted by encounters before the drag can be effective, providing the halo core radius is less than 2-4 kpc, the clusters have a size of about 1 pc, and the components of the clusters have masses less than about 10 solar masses. A variety of ways is suggested in which the clusters required in this model could arise.