The Bullet Cluster is not a Cosmological Anomaly
  The Bullet Cluster (1E0657-56) merger is of exceptional interest for testing the standard cold-dark-matter plus cosmological constant cosmological model, and for investigating the possible existence of a long- or short-range "fifth-force" in the dark sector and possible need for modifications of general relativity or even of Newtonian gravity. The most recent previous simulations of the Bullet Cluster merger required an initial infall velocity far in excess of what would be expected within the standard cosmological model, at least in the absence of additional forces or modifications to gravity. We have carried out much more detailed simulations, making pixel-by-pixel fits to 2D data-maps of the mass distribution and X-ray emission, allowing for triaxial initial configurations and including MHD and cooling. Here, we compare the initial conditions of the Bullet Cluster merger to those in similar-mass merging clusters in the Horizon cosmological simulation. We conclude that the observed properties of the Bullet Cluster are completely consistent with Lambda-CDM. 
Craig Lage and Glennys R. Farrar
astro-ph.GA