Rich clusters of galaxies, the largest virialized systems known, place powerful constraints on cosmology. Some of the fundamental questions that can be addressed with clusters of galaxies include: What is the mass-density of the universe? and how is the mass distributed? We show that several independent methods utilizing clusters of galaxies - cluster mass-to-light ratio, baryon fraction in clusters, and cluster evolution - all indicate the same robust result: the mass-density of the universe is low, Ωm≃0.25, and the mass approximately traces light on large scales. Combining the cluster results with recent observations of high-redshift supernovae and the cosmic microwave background anisotropy spectrum indicates a remarkable consistency among these independent, nearly orthogonal methods; the combined results, presented in a cosmic triangle plot, suggest a universe that is lightweight, is accelerating, and is flat.
All Science Journal Classification (ASJC) codes
- General Physics and Astronomy
- 98.80. - k
- Clusters of galaxies
- Dark matter