Astronomers have discovered the most distant “relaxed” galaxy cluster to date – the farthest cluster ever spotted that is not being disrupted by violent collisions with other clusters of galaxies. This finding is paving the way to learning how and when some of these gigantic structures form and why the universe looks like it does in the present day.
To find this distant and young galaxy cluster, teams of scientists used data from NASA’s Chandra X-ray Observatory, NASA’s retired Spitzer Space Telescope, the National Science Foundation/Department of Energy’s South Pole Telescope, and the Dark Energy Survey project in Chile. They reported the results in a series of three papers.
This galaxy cluster, called SPT-CL J2215-3537 (SPT2215 for short), is about 8.4 billion light-years from Earth, and is seen when the universe is only 5.3 billion years old, compared to its current age of 13.8 billion years. This implies that SPT2215 got a head start in its formation compared to other clusters of similar size, and that it has been undisturbed by collisions with other clusters for the last billion years, allowing it to relax. Astronomers estimate the cluster has a mass some 700 trillion times that of the Sun.
“Up until now, we have not seen a relaxed galaxy cluster as distant as SPT2215,” said Michael Calzadilla of the Massachusetts Institute of Technology (MIT), lead author of the recent paper on Astrophysical Journal, which confirmed the cluster to be relaxed and reports other key properties of the cluster. “It seems like the black hole in SPT2215 is quiet enough to let star formation flourish,” said Michael McDonald, also of MIT, who is a co-author of all three papers.
(The paper led by Bleem was published in the March 2020 issue of The Astrophysical Journal Supplement Series. The paper led by Mantz was published in the February 2022 issue of Monthly Notices of the Royal Astronomical Society, and a preprint is available online.)