Supercluster in the context of Milky Way

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 cosmology, galaxy filaments are the largest known structures in the universe, consisting of walls of galactic superclusters. These massive, thread-like formations can commonly reach 50 to 80 megaparsecs (160 to 260 megalight-years)—with the largest found to date being Quipu (400 megaparsecs), and possibly the still unconfirmed Hercules-Corona Borealis Great Wall at around 3 gigaparsecs (9.8 Gly) in length—and form the boundaries between voids. Due to the accelerating expansion of the universe, the individual clusters of gravitationally bound galaxies that make up galaxy filaments are moving away from each other at an accelerated rate; in the far future they will dissolve.

Galaxy filaments form the cosmic web and define the overall structure of the observable universe.

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 10 to 10 solar masses. Clusters consist of galaxies, heated gas, and dark matter. They are the biggest known gravitationally bound structures in the universe. They were believed to be the largest known structures in the universe until the 1980s, when superclusters were discovered. Small aggregates of galaxies are referred to as galaxy groups rather than clusters of galaxies. Together, galaxy groups and clusters form superclusters.

Cosmic voids (also known as dark space) are vast spaces between filaments (the largest-scale structures in the universe), which contain very few or no galaxies. In spite of their size, most galaxies are not located in voids. This is because most galaxies are gravitationally bound together, creating huge cosmic structures known as galaxy filaments. The cosmological evolution of the void regions differs drastically from the evolution of the universe as a whole: there is a long stage when the curvature term dominates, which prevents the formation of galaxy clusters and massive galaxies. Hence, although even the emptiest regions of voids contain more than ~15% of the average matter density of the universe, the voids look almost empty to an observer.

Voids typically have a diameter of 10 to 100 megaparsecs (30 to 300 million light-years); particularly large voids, defined by the absence of rich superclusters, are sometimes called supervoids. They were first discovered in 1978 in a pioneering study by Stephen Gregory and Laird A. Thompson at the Kitt Peak National Observatory.

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.

In physics, a redshift is an increase in the wavelength, or equivalently, a decrease in the frequency, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and energy, is known as a blueshift.

Three forms of redshift occur in astronomy and cosmology: Doppler redshifts due to the relative motions of radiation sources, gravitational redshift as radiation escapes from gravitational potentials, and cosmological redshifts caused by the universe expanding. In astronomy, the value of a redshift is often denoted by the letter z, corresponding to the fractional change in wavelength (positive for redshifts, negative for blueshifts), and by the wavelength ratio 1 + z (which is greater than 1 for redshifts and less than 1 for blueshifts). Automated astronomical redshift surveys are an important tool for learning about the large-scale structure of the universe. Redshift and blueshift can also be related to photon energy and, via Planck's law, to a corresponding blackbody temperature.

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.

The Laniakea Supercluster or Laniakea for short (/ˌlɑːni.əˈkeɪ.ə/; Hawaiian for "open skies" or "immense heaven"), sometimes also called the Local Supercluster (LSC or LS), is the large-scale structure centered around the Great Attractor that is home to the Milky Way and approximately 100,000 other nearby galaxies. It was originally defined in September 2014 as a galaxy supercluster, when a group of astronomers, including R. Brent Tully of the University of Hawaiʻi at Mānoa, Hélène Courtois of the University of Lyon, Yehuda Hoffman of the Hebrew University of Jerusalem, and Daniel Pomarède of CEA Université Paris-Saclay published a new way of defining superclusters according to the relative velocities of galaxies as basins of attraction. The new definition of the local supercluster subsumes the then prior defined Virgo and Hydra-Centaurus Supercluster as appendages, the former being the prior defined local supercluster.

Follow-up studies suggest that the Laniakea is not gravitationally bound. It will disperse rather than continue to maintain itself as an overdensity relative to surrounding areas. In addition, some papers favored the traditional definition of superclusters as high-density regions of the cosmic web; basins of attraction including Laniakea were therefore proposed to be called "supercluster cocoons" (or "cocoons" for short), containing smaller traditional superclusters, which evolve inside their parent cocoon.

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.

Galaxy groups and clusters are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation. They form the densest part of the large-scale structure of the Universe. In models for the gravitational formation of structure with cold dark matter, the smallest structures collapse first and eventually build the largest structures, clusters of galaxies. Clusters are then formed relatively recently between 10 billion years ago and now. Groups and clusters may contain ten to thousands of individual galaxies. The clusters themselves are often associated with larger, non-gravitationally bound, groups called superclusters.

The Pisces–Cetus Supercluster Complex (Pisces–Cetus SCC) or the local superstructure is a galaxy supercluster complex (SCC) that includes the Virgo Supercluster as its outlying member (later confirmed to be part of the Laniakea), which in turn contains the Local Group, the galaxy group that includes the Milky Way. The complex was named after the Pisces–Cetus Superclusters, which are its richest and most prominent superclusters and reside in as its core and of its main plane, located at roughly 200 megaparsecs (652 million light-years; 6.17×10 kilometres) away from Earth. A supercluster complex is defined as container of several dozens of rich clusters and large superclusters.

This filament is adjacent to the Perseus–Pegasus Filament.

In cosmology, galaxy filaments are the largest known structures in the universe, consisting of walls of galactic superclusters. These massive, thread-like formations can commonly reach 50 to 80 megaparsecs (160 to 260 megalight-years)—with the largest found to date being Quipu (400 megaparsecs), and possibly the still unconfirmed Hercules–Corona Borealis Great Wall at around 3 gigaparsecs (9.8 Gly) in length—and form the boundaries between voids. Due to the accelerating expansion of the universe, the individual clusters of gravitationally bound galaxies that make up galaxy filaments are moving away from each other at an accelerated rate; in the far future they will dissolve.

Galaxy filaments form the cosmic web and define the overall structure of the observable universe.

The large-scale structure of the universe is the term in cosmology for the character of matter distribution at the scale of the entire observable universe.Sky surveys and mappings of the various wavelength bands of electromagnetic radiation (in particular 21-cm emission) have yielded much information on the content and character of the universe's structure. The organization of structure appears to follow a hierarchical model with organization up to the scale of superclusters and filaments. Larger than this (at scales between 30 and 200 megaparsecs), there seems to be no continued structure, a phenomenon that has been referred to as the End of Greatness. The shape of the large scale structure can be summarized by the matter power spectrum.

In physics, a redshift is an increase in the wavelength, or equivalently, a decrease in the frequency, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and energy, is known as a blueshift.

Three forms of redshift occur in astronomy and cosmology: Doppler redshifts due to the relative motions of radiation sources, gravitational redshift as radiation escapes from gravitational potentials, and cosmological redshifts caused by the universe expanding. The value of a redshift is often denoted by the letter z, corresponding to the fractional change in wavelength (positive for redshifts, negative for blueshifts), and by the wavelength ratio 1 + z (which is greater than 1 for redshifts and less than 1 for blueshifts). Automated astronomical redshift surveys are an important tool for learning about the large-scale structure of the universe. Redshift and blueshift can also be related to photon energy and, via Planck's law, to a corresponding blackbody temperature.