What X-rays tell us about dark matter halos

We present a detailed non-spherical modeling of dark matter halos on the basis of a careful analysis of state-of-the art N-body simulations. The fitting formulae presented here form a complete and accurate description of the triaxial density profiles of halos in Cold Dark Matter(CDM) models. This modeling allows us to quantitatively discuss implications for shape observations of galactic and cluster halos. The predictions of the concordance $\lambda$CDM model are confronted with the shape observations from the Milky Way to X-ray clusters.