  Starting from the effective action of the low energy limit of superstrings
theory, I find an exact solution of the field equations which geodesics behavie
exactly as the trajectories of stars arround of a spiral galaxy. Here dark
matter is of dilatonic origin. It is remarkable that the energy density of this
space-time is the same as the used by astronomers to model galaxy stability.
Some remarks about a universe dominated by dilatons are pointed out.
