A gravitational lens is matter, such as a cluster of galaxies or a point particle, that bends light from a distant source as it travels toward an observer. The amount of gravitational lensing is described by Albert Einstein's general theory of relativity. If light is treated as corpuscles travelling at the speed of light, Newtonian physics also predicts the bending of light, but only half of that predicted by general relativity.
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.
Abell 2218 is a large cluster of galaxies over 2 billion light-years away in the constellation Draco.
Abell 1835 is a galaxy cluster in the Abell catalogue. It is a cluster that also gravitational lenses more-distant background galaxies to make them visible to astronomers. The cluster has a red shift of around 75,900 km/s and spans 12′.
The Coma Cluster is a large cluster of galaxies that contains over 1,000 identified galaxies. Along with the Leo Cluster, it is one of the two major clusters comprising the Coma Supercluster. It is located in and takes its name from the constellation Coma Berenices.
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.
IC 1101 is a class S0 supergiant (cD) lenticular galaxy at the center of the Abell 2029 galaxy cluster. It has an isophotal diameter at about 123.65 to 169.61 kiloparsecs. It possesses a diffuse core which is the largest known core of any galaxy to date, and contains a supermassive black hole, one of the largest discovered. IC 1101 is located at 354.0 megaparsecs from Earth. It was discovered on 19 June 1790, by the British astronomer William Herschel.
Abell 1689 is a galaxy cluster in the constellation Virgo over 2.3 billion light-years away.
Abell 2667 is a galaxy cluster. It is one of the most luminous galaxy clusters in the X-ray waveband known at a redshift about 0.2.
The Hercules Cluster is a cluster of about 200 galaxies some 500 million light-years distant in the constellation Hercules. It is rich in spiral galaxies and shows many interacting galaxies. The cluster is part of the larger Hercules Supercluster, which is itself part of the much larger Great Wall super-structure.
Abell 520 is a galaxy cluster in the Orion constellation, located at a co-moving radial distance of 811 Mpc (2,645 Mly) and subtends 25 arcminutes on the Earth sky.
The Leo Cluster is a galaxy cluster about 330 million light-years distant in the constellation Leo, with at least 70 major galaxies. The galaxy known as NGC 3842 is the brightest member of this cluster. Along with the Coma Cluster, it is one of the two major clusters comprising the Coma Supercluster, which in turn is part of the CfA2 Great Wall, which is hundreds of millions light years long and is one of the largest known structures in the universe.
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 2744, nicknamed Pandora's Cluster, is a giant galaxy cluster resulting from the simultaneous pile-up of at least four separate, smaller galaxy clusters that took place over a span of 350 million years, and is located approximately 4 billion light years from Earth. The galaxies in the cluster make up less than five percent of its mass. The gas is so hot that it shines only in X-rays. Dark matter makes up around 75 percent of the cluster's mass.
Abell 1413 is a massive and rich type I galaxy cluster straddling the border between the constellations Leo and Coma Berenices, with the projected comoving distance of approximately 640 Mpc (2.1 billion ly). The cluster is especially notable due to the presence of its very large brightest cluster galaxy (BCG), one of the most extreme examples of its type, as well as one of the largest galaxies known. The cluster was first noted by George O. Abell in 1958.
Abell 222 is a galaxy cluster in the constellation of Cetus. It holds thousands of galaxies together. It is located at a distance of 2.4 billion light-years from Earth.
Abell 2152 is a bimodal galaxy cluster and one of three clusters comprising the Hercules Supercluster. It contains 3 BCGs; the S0 lenticular UGC 10204, the pair UGC 10187, and the SA0 unbarred lenticular CGCG 108-083. In total there are 41 galaxies which are confirmed to be members of the cluster. The cluster is classified as a Bautz-Morgan type III and Rood-Sastry class F cluster, indicating morphological irregularity and perhaps dynamical youth. It is receding from the Milky Way galaxy with a velocity of 12385 km/s.
MACS J1149 Lensed Star 1, also known as Icarus, is a blue supergiant star observed through a gravitational lens. It is the seventh most distant individual star to have been detected so far, at approximately 14 billion light-years from Earth. Light from the star was emitted 4.4 billion years after the Big Bang. According to co-discoverer Patrick Kelly, the star is at least a hundred times more distant than the next-farthest non-supernova star observed, SDSS J1229+1122, and is the first magnified individual star seen.
WHL0137-LS, also known as Earendel, is a star located in the constellation of Cetus. Discovered in 2022 by the Hubble Space Telescope, it is the earliest and most distant known star, at a comoving distance of 28 billion light-years. The previous furthest known star, MACS J1149 Lensed Star 1, also known as Icarus, at a comoving distance of 14.4 billion light-years, was discovered by Hubble in 2018. Stars like Earendel can be observed at cosmological distances thanks to the large magnification factors afforded by gravitational lensing, which can exceed 1,000. Other stars have been observed through this technique, such as Godzilla.
SMACS J0723.3–7327, commonly referred to as SMACS 0723, is a galaxy cluster about 4 billion light years from Earth, within the southern constellation of Volans. It is a patch of sky visible from the Southern Hemisphere on Earth and often observed by the Hubble Space Telescope and other telescopes in search of the deep past. It was the target of the first full-color image to be unveiled by the James Webb Space Telescope (JWST), imaged using NIRCam, with spectra included, showing objects lensed by the cluster with redshifts implying they are 13.1 billion years old. The cluster has been previously observed by the Hubble Space Telescope (HST) as part of the Southern MAssive Cluster Survey (SMACS), as well as Planck and Chandra.
