Galaxies are huge collections of stars, gas, dust and dark matter bound together by gravity. They are not randomly distributed throughout space; they can be concentrated in certain areas known as clusters, or absent in areas known as voids. Other more complex distributions are also known to exist. Some of the largest and earliest galaxies reside within clusters. It is believed that through unveiling information about early universe galaxy clusters we may be able to further our knowledge of the lifecycles of ancient galaxies, but these structures are rare which has hindered efforts in the past.

Since 2006, a team of astrophysicists have been studying a suspected distant cluster known as JKCS 041, but they struggled to confirm how far away it is. Now, in a paper published in The Astrophysical Journal, scientists led by Carnegie’s Andrew Newman have confirmed the presence of this unusually distant cluster using Hubble Space Telescope data. The researchers discovered 19 close galaxies which are all 9.9 billion light years away, suggesting they represent an early universe cluster.

Previous data collected from the Chandra X-ray Observatory found X-ray emissions within the JKCS 041 vicinity. “These X-rays likely originate from hot gas in JKCS 041, which has been heated to a temperature of about 80 million degrees by the gravity of the massive cluster,” said Stefano Andreon, one of the authors of the study, in a news-release.

The biggest and oldest known galaxies in the universe reside within clusters, but there remains some uncertainty as to why star formation came to a halt in these galactic monsters, resulting in a dormant phase. By observing the galaxies within the JKCS 041 cluster when they were a mere 1 billion years old, or 10% of their current age, the researchers discovered that the majority were already dormant.

When large galaxies enter this dormant phase they are still able to grow by merging with other galaxies that they collide with. It’s thought that this would be a common occurrence in early universe galaxies; however, the researchers discovered that JKCS 041’s galaxies were expanding at a similar rate to galaxies not in clusters.

“Because JKCS 041 is the most distant-known cluster of its size, it gives us a unique opportunity to study these old galaxies in detail and better understand their origins,” said Newman. “Our observations make this galaxy cluster one of the best studied structures from the early universe.”