Galaxy cluster in the context of Coma Cluster

The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from sub-atomic particles to entire galactic filaments. Since the early 20th century, the field of cosmology establishes that space and time emerged together at the Big Bang 13.787±0.020 billion years ago and that the universe has been expanding since then. The portion of the universe that can be seen by humans is approximately 93 billion light-years in diameter at present, but the total size of the universe is not known.

Some of the earliest cosmological models of the universe were geocentric, placing Earth at the center. During the European Renaissance, astronomical observations led to heliocentric models.Further observational improvements led to the realization that the Sun is one of a few hundred billion stars in the Milky Way, which is one of a few hundred billion galaxies in the observable universe. Many of the stars in a galaxy have planets. At the largest scale, galaxies are distributed uniformly and the same in all directions, meaning that the universe has neither an edge nor a center. At smaller scales, galaxies are distributed in clusters and superclusters which form immense filaments and voids in space, creating a vast foam-like structure. Discoveries in the early 20th century lead to the Big Bang theory with a hot fireball, cooling and becoming less dense as the universe expanded, allowing the first subatomic particles and simple atoms to form. Giant clouds of hydrogen and helium were gradually drawn to the places where matter was most dense, forming the first galaxies, stars, and everything else seen today.

In astronomy and cosmology, dark matter is an invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravitational effects that cannot be explained by general relativity unless more matter is present than can be observed. Such effects occur in the context of formation and evolution of galaxies, gravitational lensing, the observable universe's current structure, mass position in galactic collisions, the motion of galaxies within galaxy clusters, and cosmic microwave background anisotropies. Dark matter is thought to serve as gravitational scaffolding for cosmic structures.After the Big Bang, dark matter clumped into blobs along narrow filaments with superclusters of galaxies forming a cosmic web at scales on which entire galaxies appear like tiny particles.

Observations show that the expansion of the universe is accelerating, such that the velocity at which a distant galaxy recedes from the observer is continuously increasing with time. The accelerated expansion of the universe was discovered in 1998 by two independent projects, the Supernova Cosmology Project and the High-Z Supernova Search Team, which used distant type Ia supernovae to measure the acceleration. The idea was that as type Ia supernovae have almost the same intrinsic brightness (a standard candle), and since objects that are further away appear dimmer, the observed brightness of these supernovae can be used to measure the distance to them. The distance can then be compared to the supernovae's cosmological redshift, which measures how much the universe has expanded since the supernova occurred; the Hubble law established that the further away an object is, the faster it is receding. The unexpected result was that objects in the universe are moving away from one another at an accelerating rate. Cosmologists at the time expected that recession velocity would always be decelerating, due to the gravitational attraction of the matter in the universe. Three members of these two groups have subsequently been awarded Nobel Prizes for their discovery. Confirmatory evidence has been found in baryon acoustic oscillations, and in analyses of the clustering of galaxies.

The accelerated expansion of the universe is thought to have begun since the universe entered its dark-energy-dominated era roughly 5 billion years ago.Within the framework of general relativity, an accelerated expansion can be accounted for by a positive value of the cosmological constant Λ, equivalent to the presence of a positive vacuum energy, dubbed "dark energy". While there are alternative possible explanations, the description assuming dark energy (positive Λ) is used in the standard model of cosmology, which also includes cold dark matter (CDM) and is known as the Lambda-CDM model.

A supercluster is a large group of smaller galaxy clusters or galaxy groups; they are among the largest known structures in the universe. The Milky Way is part of the Local Group galaxy group (which contains more than 54 galaxies), which in turn is part of the Virgo Supercluster, which is part of the Laniakea Supercluster, which is part of the Pisces–Cetus Supercluster Complex. The large size and low density of superclusters means that most of them, unlike clusters, expand with the Hubble expansion. The number of superclusters in the observable universe is estimated to be 10 million.

The type-cD galaxy (also cD-type galaxy, cD galaxy) is a galaxy morphology classification, a subtype of type-D giant elliptical galaxy. Characterized by a large halo of stars, they can be found near the centres of some rich galaxy clusters. They are also known as supergiant ellipticals or central dominant galaxies.

An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the three main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work The Realm of the Nebulae, along with spiral and lenticular galaxies. Elliptical (E) galaxies are, together with lenticular galaxies (S0) with their large-scale disks, and ES galaxies with their intermediate scale disks, a subset of the "early-type" galaxy population.

Most elliptical galaxies are composed of older, low-mass stars, with a sparse interstellar medium, and they tend to be surrounded by large numbers of globular clusters. Star formation activity in elliptical galaxies is typically minimal; they may, however, undergo brief periods of star formation when merging with other galaxies. Elliptical galaxies are believed to make up approximately 10–15% of galaxies in the Virgo Supercluster, and they are not the dominant type of galaxy in the universe overall. They are preferentially found close to the centers of galaxy clusters.

The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from sub-atomic particles to entire galactic filaments. Since the early 20th century, the field of cosmology establishes that space and time emerged together at the Big Bang 13.787±0.020 billion years ago and that the universe has been expanding since then. The portion of the universe that can be seen by humans is approximately 93 billion light-years in diameter at present, but the total size of the universe is not known.

Some of the earliest cosmological models of the universe were geocentric, placing Earth at the center. During the European Scientific Revolution, astronomical observations led to a heliocentric model. Further observational improvements led to the realization that the Sun is one of a few hundred billion stars in the Milky Way, which is one of a few hundred billion galaxies in the observable universe. Many of the stars in a galaxy have planets. At the largest scale, galaxies are distributed uniformly and the same in all directions, meaning that the universe has neither an edge nor a center. At smaller scales, galaxies are distributed in clusters and superclusters which form immense filaments and voids in space, creating a vast foam-like structure. Discoveries in the early 20th century lead to the Big Bang theory with a hot fireball, cooling and becoming less dense as the universe expanded, allowing the first subatomic particles and simple atoms to form. Giant clouds of hydrogen and helium were gradually drawn to the places where matter was most dense, forming the first galaxies, stars, and everything else seen today.

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.

Orest Khvolson (1924) and Frantisek Link (1936) are generally credited with being the first to discuss the effect in print, but it is more commonly associated with Einstein, who made unpublished calculations on it in 1912 and published an article on the subject in 1936.

In physical cosmology, structure formation describes the creation of galaxies, galaxy clusters, and larger structures via gravitational and hydrodynamic processes operating on cosmological inhomogeneities. The universe, as is now known from observations of the cosmic microwave background radiation, began in a hot, dense, nearly uniform state approximately 13.8 billion years ago. However, looking at the night sky today, structures on all scales can be seen, from stars and planets to galaxies. On even larger scales, galaxy clusters and sheet-like structures of galaxies are separated by enormous voids containing few galaxies. Structure formation applies models of gravitational instability to small ripples in mass density to predict these shapes.

The modern Lambda-CDM model is successful at predicting the observed large-scale distribution of galaxies, clusters and voids; but on the scale of individual galaxies there are many complications due to highly nonlinear processes involving baryonic physics, gas heating and cooling, star formation and feedback. Understanding the processes of galaxy formation is a major topic of modern cosmology research, both via observations such as the Hubble Ultra-Deep Field and via large computer simulations.

A satellite galaxy is a smaller companion galaxy that travels on bound orbits within the gravitational potential of a more massive and luminous host galaxy (also known as the primary galaxy). Satellite galaxies and their constituents are bound to their host galaxy, in the same way that planets within the Solar System are gravitationally bound to the Sun. While most satellite galaxies are dwarf galaxies, satellite galaxies of large galaxy clusters can be much more massive. The Milky Way is orbited by about fifty satellite galaxies, the largest of which is the Large Magellanic Cloud.

Moreover, satellite galaxies are not the only astronomical objects that are gravitationally bound to larger host galaxies (see globular clusters). For this reason, astronomers have defined galaxies as gravitationally bound collections of stars that exhibit properties that cannot be explained by a combination of baryonic matter (i.e. ordinary matter) and Newton's laws of gravity. For example, measurements of the orbital speed of stars and gas within spiral galaxies result in a velocity curve that deviates significantly from the theoretical prediction. This observation has motivated various explanations such as the theory of dark matter and modifications to Newtonian dynamics. Therefore, despite also being satellites of host galaxies, globular clusters should not be mistaken for satellite galaxies. Satellite galaxies are not only more extended and diffuse compared to globular clusters, but are also enshrouded in massive dark matter halos that are thought to have been endowed to them during the formation process.

The gravitational binding energy of a system is the minimum energy which must be added to it in order for the system to cease being in a gravitationally bound state. A gravitationally bound system has a lower (i.e., more negative) gravitational potential energy than the sum of the energies of its parts when these are completely separated—this is what keeps the system aggregated in accordance with the minimum total potential energy principle.

Quipu is a large-scale superstructure of galaxies of the Universe, a wall of galaxies or galaxy hypercluster composed of knots of galaxy clusters. As of 2025, it is the largest known structure in the Universe, some 1.3 billion light years long (1.3×10 light-years (7.6×10 mi; 1.2×10 km)); and the most massive known structure, containing 2×10 solar masses (4.0×10 kg; 8.8×10 lb; 4.0×10 t),or about 200,000 times the mass of the Milky Way.

The structure was discovered by Hans Böhringer and colleagues using data from the ROSAT X-ray satellite, and described in a 2025 paper on arXiv. It was named "quipu" as it is reminiscent of the Andean knotted textile called quipu that Böhringer had seen in a museum near Santiago, Chile, while he was working at the European Southern Observatory.

The Local Supercluster (LSC or LS) is a supercluster of galaxies containing the Virgo Cluster and Local Group. The latter contains the Milky Way and Andromeda galaxies, among others. Sometimes referred to as Virgo Supercluster, the Local Supercluster is roughly centered on the Virgo Cluster, with the Local Group located near one edge and revolving around its center.

At least 100 galaxy groups and clusters are located within the supercluster diameter of 45 megaparsecs (147 million light-years; 1.39×10 kilometres). The Local Supercluster is one of about 10 million superclusters in the observable universe, with the main body of the supercluster, the Virgo Strand, connecting the Hydra-Centaurus and the Perseus–Pisces Superclusters. It is part of the Pisces–Cetus Supercluster Complex, a very large galaxy filament.

BoRG-58 is a galaxy cluster located in the Boötes constellation. It was discovered during a randomized infrared sky scan as part of the Brightest of Reionizing Galaxies (BoRG) program, using the Wide Field Camera 3 of the Hubble Space Telescope. BoRG-58 is located at a distance of 13.1 billion light-years (light-travel time).

In the cluster, more properly defined as a protocluster of galaxies, five young galaxies have been identified whose images date back to an era corresponding to when the Universe was only 600 million years old from the Big Bang. This phase coincides with the epoch of reionization, the period during which the hydrogen of the gas present in the Universe passed from an almost completely neutral state to being almost completely ionized. These five galaxies were small in size, about 1/20 of the Milky Way, but nevertheless had a luminosity comparable to it.

A galaxy group or group of galaxies (GrG) is an aggregation of galaxies comprising about 50 or fewer gravitationally bound members, each at least as luminous as the Milky Way (about 10 times the luminosity of the Sun); collections of galaxies larger than groups that are first-order clustering are called galaxy clusters. The groups and clusters of galaxies can themselves be clustered, into superclusters of galaxies.

The Milky Way galaxy is part of a group of galaxies called the Local Group.

A void galaxy is a galaxy located in a cosmological void. Few galaxies exist in voids; most are located in sheets, walls and filaments that surround voids and supervoids. Many void galaxies are connected through void filaments or tendrils, less massive versions of the regular galaxy filaments that surround voids. These filaments are often straighter than their non-void counterparts due to the lack of influence by surrounding filaments. These filaments can even be rich enough to form poor galaxy clusters. The void galaxies themselves are thought to represent pristine examples of galactic evolution, having few neighbours, and likely to have formed from pure intergalactic gas.

ESO 383-76 (ESO 383-G 076) is an elongated, X-ray luminous supergiant elliptical galaxy, residing as the dominant, brightest cluster galaxy (BCG) of the Abell 3571 galaxy cluster, the sixth-brightest in the sky at X-ray wavelengths. It is located at the distance of 200.6 megaparsecs (654 million light-years) from Earth, and is possibly a member of the large Shapley Supercluster. With a diameter of about 540.9 kiloparsecs (1.8 million light-years), it is one of the largest galaxies known. It also contains a supermassive black hole, one of the most massive known with mass estimates varying from 2 billion M_☉ to 28 billion M_☉.