How the first groups of galaxies formed is one of the biggest mysteries in modern cosmology. Now another piece of the puzzle has been identified by the Very Large Telescope (VLT) in Chile, with the discovery of a cluster of 20 galaxies at a redshift of 4.1. This is the furthest cluster of galaxies ever observed.
Studies of early galaxy clusters provide an important constraint for theories of galactic evolution, but they are extremely difficult to detect. The new observations focused on areas around known radio galaxies (galaxies with particularly strong radio emission). Radio galaxies are excellent tracers for early galaxy formation, as they are found in high-density regions of the early universe that evolve into present-day clusters.
The tactics paid off. The 20 galaxies that were discovered belong to a group that measures approximately 10 million light-years across. This “proto-cluster” confirms that large-scale structures had already formed when the universe was about a tenth of its present age.
