Baryons at the Edge of the X-ray Brightest Galaxy Cluster
  Studies of the diffuse X-ray emitting gas in galaxy clusters have provided
powerful constraints on cosmological parameters and insights into plasma
astrophysics. However, measurements of the faint cluster outskirts have become
possible only recently. Using data from the Suzaku X-ray telescope, we
determined an accurate, spatially resolved census of the gas, metals, and dark
matter out to the edge of the Perseus Cluster. Contrary to previous results,
our measurements of the cluster baryon fraction are consistent with the
expected universal value at half of the virial radius. The apparent baryon
fraction exceeds the cosmic mean at larger radii, suggesting a clumpy
distribution of the gas, which is important for understanding the ongoing
growth of clusters from the surrounding cosmic web.
