A galaxy cluster, or a cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity, with typical masses ranging from 1014 to 1015 solar masses. They are the second-largest known gravitationally bound structures in the universe after some superclusters (of which only one, the Shapley Supercluster, is known to be bound). They were believed to be the largest known structures in the universe until the 1980s, when superclusters were discovered. One of the key features of clusters is the intracluster medium (ICM). The ICM consists of heated gas between the galaxies and has a peak temperature between 2–15 keV that is dependent on the total mass of the cluster. Galaxy clusters should not be confused with galactic clusters (also known as open clusters), which are star clusters within galaxies, or with globular clusters, which typically orbit galaxies. Small aggregates of galaxies are referred to as galaxy groups rather than clusters of galaxies. The galaxy groups and clusters can themselves cluster together to form superclusters.
Lynx is a constellation named after the animal, usually observed in the Northern Celestial Hemisphere. The constellation was introduced in the late 17th century by Johannes Hevelius. It is a faint constellation, with its brightest stars forming a zigzag line. The orange giant Alpha Lyncis is the brightest star in the constellation, and the semiregular variable star Y Lyncis is a target for amateur astronomers. Six star systems have been found to contain planets. Those of 6 Lyncis and HD 75898 were discovered by the Doppler method; those of XO-2, XO-4, XO-5 and WASP-13 were observed as they passed in front of the host star.
The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the Space ShuttleColumbia during STS-93 by NASA on July 23, 1999. Chandra was sensitive to X-ray sources 100 times fainter than any previous X-ray telescope, enabled by the high angular resolution of its mirrors. Since the Earth's atmosphere absorbs the vast majority of X-rays, they are not detectable from Earth-based telescopes; therefore space-based telescopes are required to make these observations. Chandra is an Earth satellite in a 64-hour orbit, and its mission is ongoing as of 2024.
The Perseus cluster is a cluster of galaxies in the constellation Perseus. It has a recession speed of 5,366 km/s and a diameter of 863′. It is one of the most massive objects in the known universe, containing thousands of galaxies immersed in a vast cloud of multimillion-degree gas.
Amy J. Barger is an American astronomer and Henrietta Leavitt Professor of Astronomy at the University of Wisconsin–Madison. She is considered a pioneer in combining data from multiple telescopes to monitor multiple wavelengths and in discovering distant galaxies and supermassive black holes, which are outside of the visible spectrum. Barger is an active member of the International Astronomical Union.
XMMXCS 2215-1738 is a galaxy cluster that lies 10 billion light-years away and has a redshift value of z=1.45. It was discovered by the XMM Cluster Survey in 2006.
3C 295 is a narrow-line radio galaxy located in the constellation of Boötes. With a redshift of 0.464, it is approximately 5 billion light-years from Earth. At time of the discovery of its redshift in 1960, this was the remotest object known.
2XMM J083026+524133 is a very large galaxy cluster that lies 7.7 billion light-years away. It was discovered by chance by ESA's XMM Newton and the Large Binocular Telescope (LBT) in Arizona in 2008 while it was looking at the quasar APM 08279+5255.
Abell 2142, or A2142, is a huge, X-ray luminous galaxy cluster in the constellation Corona Borealis. It is the result of a still ongoing merger between two galaxy clusters. The combined cluster is six million light years across, contains hundreds of galaxies and enough gas to make a thousand more. It is "one of the most massive objects in the universe."
Abell 370 is a galaxy cluster located nearly 5 billion light-years away from the Earth, in the constellation Cetus. Its core is made up of several hundred galaxies. It was catalogued by George Abell, and is the most distant of the clusters he catalogued.
JKCS 041 is a cluster of galaxies with the distinction, as of 2009, of being the farthest galaxy cluster observed from Earth. It is estimated to be 10.2 billion light-years away, seen at redshift 1.9. The cluster is located in the constellation Cetus at a photometrically determined redshift of z=1.9 at right ascension 2h 26m 44s declination −04° 41′ 37″ (J2000.0). There are at least 19 members in the cluster.
El Gordo (lit. The Fat One) (ACT-CL J0102-4915 or SPT-CL J0102-4915) is the largest distant galaxy cluster observed at its distance or beyond, as of 2011. As of 2014, it held the record for being the largest distant galaxy cluster to have been discovered with a mass of slightly less than three quadrillion solar masses although later its mass was reduced to about 2.1×1015 (2.1 quadrillion) solar masses with a 10% uncertainty. It was found by NASA's Chandra X-ray Observatory, the Atacama Cosmology Telescope (funded by the National Science Foundation) and the European Southern Observatory's Very Large Telescope.
MACS0647-JD is a galaxy with a redshift of about z = 10.7, equivalent to a light travel distance of 13.26 billion light-years. If the distance estimate is correct, it formed about 427 million years after the Big Bang.
The Cluster Lensing And Supernova survey with Hubble (CLASH) was a program on the Hubble Space Telescope to observe 25 massive galaxy clusters. CLASH was one of three programs selected in the first class of Hubble multi-cycle treasury programs, which were designed to tackle large questions unanswerable through normal observations. Observations for CLASH were conducted between November 2010 and July 2013. CLASH was led by principal investigator Marc Postman, and had a science team of over 40 researchers.
The galaxy cluster IRC 0218 hosts the most distant strong gravitational lensing galaxy currently known at a redshift of z = 1.62. The lens is one of the two brightest cluster galaxies and is lensing a background star-forming galaxy at a redshift of z = 2.26 into a bright arc and a faint counterimage. The lens was discovered through a combination of Hubble Space Telescope and Keck telescope imaging and spectroscopy. The discovery and subsequent analysis of the lens was published in the Astrophysical Journal Letters on June 23, 2014 by an international team of astronomers led by Dr. Kim-Vy Tran from Texas A&M University in College Station, Texas and team members Dr. Kenneth Wong and Dr. Sherry Suyu from the Academia Sinica Institute of Astronomy and Astrophysics in Taipei, Taiwan.
CL J1001+0220 is, as of 2016, the most distant known galaxy cluster. Discovered in 2016 by the Chandra X-ray Observatory in conjunction with the ESO's UltraVISTA telescope and the Atacama Large Millimeter Array, it has a redshift of z=2.506, placing it at a distance of 11.1 billion light-years from Earth. The galaxy cluster appears to be undergoing the transformation from a galaxy cluster that is still forming, a proto-cluster, to a mature cluster, and it is the first such cluster observed in this stage of its evolution.
UHZ1 is a background galaxy containing a quasar. At a redshift of approximately 10.1, UHZ1 is at a distance of 13.2 billion light-years, seen when our universe was about 3 percent of its current age. This redshift made it the most distant, and therefore earliest known quasar in the observable universe as of 2023. To detect this object, astronomers working at the Chandra X-ray Observatory used the Abell 2744's cluster mass as a gravitational lens in order to magnify distant objects directly behind it. At the time of discovery, it exceeded the distance record of QSO J0313−1806.
