Galactic Halos are Einstein Clusters of WIMPs

It is shown that an Einstein cluster of WIMPs, WIMPs on stable circular geodesic orbits generating the static spherically symmetric gravitational field of a galactic halo, can exactly reproduce the rotation curve of any galaxy simply by adjusting the local angular momentum distribution and consequent number distribution of the WIMPs. No new physics is involved (assuming the forthcoming discovery of WIMPs). Further, stability of the orbits can require an inner truncation of the halo and an explicit example of this is given. There is no exact Newtonian counterpart to the model presented since pure Newtonian gravity fails to account for the contribution made by the angular momentum distribution of the particles in creating the gravitational field. In effect, a galactic halo is supported by the hoop stresses created by the orbiting WIMPs.