  X-ray observations of galaxy clusters potentially provide powerful
cosmological probes if systematics due to our incomplete knowledge of the
intracluster medium (ICM) physics are understood and controlled. In this paper,
we study the effects of galaxy formation on the properties of the ICM and X-ray
observable-mass relations using high-resolution self-consistent cosmological
simulations of galaxy clusters and comparing their results with recent Chandra
X-ray observations. We show that despite complexities of their formation and
uncertainties in their modeling, clusters of galaxies both in observations and
numerical simulations are remarkably regular outside of their cores, which
holds great promise for their use as cosmological probes.
