Discovered in 2006, XMMXCS 2215-1738 is one of the most distant galaxy clusters known. It is embedded in intergalactic gas that has a temperature of 10 million degrees.[2] The estimated mass of the cluster is 500 trillion solar masses, most coming from dark matter. The cluster was discovered and studied using the XMM-Newton and Keck Telescopes. The cluster is surprisingly large and evolved for a cluster that existed when the universe was only 3 billion years old.[1][3]
It contains hundreds of reddish galaxies surrounded by x-ray-emitting gas.[4]
"The existence of the cluster so early in the history of the universe challenges ideas about how galaxies formed"
— Adam Stanford, research scientist at UC Davis and the Lawrence Livermore National Laboratory.[5]
The galaxy is called XMMXCS 2215-1734 in many references, with some news sources listing both names. The source of the naming contradiction between XMMXCS 2215-1734 and XMMXCS 2215-1738 is not known. However, XMMXCS 2215-1738 seems to be the more accurate.[citation needed]
