Magazine article Science News

Distant Cluster Suggests Low-Weight Cosmos

Magazine article Science News

Distant Cluster Suggests Low-Weight Cosmos

Article excerpt

Lured by the radio beacon of a faraway galaxy, astronomers have discovered the most distant cluster of galaxies known in the universe. The group lies 10 billion light-years from Earth and provides a snapshot of what a large collection of galaxies looked like when the cosmos was still in its youth.

The distant cluster also provides new evidence that the density of matter is lower than the so-called critical density, the value required to keep the universe flat. Above or below that density, the universe has to have a curved geometry, notes study coauthor Andrew C. Fabian of the University of Cambridge in England. He and his Cambridge colleagues Carolin S. Crawford, Stefano Ettori, and Jeremy S. Sanders will report their findings in an upcoming MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY.

To search for distant clusters, the team scoured the heavens for a signpost: The gas surrounding large groups of galaxies emits a diffuse, X-ray glow. Even so, says Fabian, the team would have had to examine thousands of images taken by NASAs Chandra X-ray Observatory to find such a signpost. So the researchers sought out another indicator. In nearby reaches of the universe, galaxies that emit powerful radio waves tend to reside in clusters. The team predicted the same would hold for powerful radio emitters in more distant parts of the cosmos.

Aiming Chandra at the radio-loud galaxy 3C294, 10 billion light-years from Earth, the astronomers struck gold. They found the signature X-ray glow indicating the distant body was part of a cluster. …

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