In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation. The opposite change, a decrease in wavelength and increase in frequency and energy, is known as a blueshift, or negative redshift. The terms derive from the colours red and blue which form the extremes of the visible light spectrum. The main causes of electromagnetic redshift in astronomy and cosmology are the relative motions of radiation sources, which give rise to the relativistic Doppler effect, and gravitational potentials, which gravitationally redshift escaping radiation. All sufficiently distant light sources show cosmological redshift corresponding to recession speeds proportional to their distances from Earth, a fact known as Hubble's law that implies the universe is expanding.
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 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 they, unlike clusters, expand with the Hubble expansion. The number of superclusters in the observable universe is estimated to be 10 million.
The following is a timeline of galaxies, clusters of galaxies, and large-scale structure of the universe.
The Local Supercluster is a formerly defined supercluster containing the Virgo Cluster and Local Group, which itself contains the Milky Way and Andromeda galaxies, as well as others. At least 100 galaxy groups and clusters are located within its diameter of 33 megaparsecs. The Virgo SC is one of about 10 million superclusters in the observable universe and is in the Pisces–Cetus Supercluster Complex, a galaxy filament.
The Great Attractor is a region of gravitational attraction in intergalactic space and the apparent central gravitational point of the Laniakea Supercluster of galaxies that includes the Milky Way galaxy, as well as about 100,000 other galaxies.
The observable universe is a ball-shaped region of the universe consisting of all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time; the electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. Initially, it was estimated that there may be 2 trillion galaxies in the observable universe. That number was reduced in 2021 to several hundred billion based on data from New Horizons. Assuming the universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction. That is, the observable universe is a spherical region centered on the observer. Every location in the universe has its own observable universe, which may or may not overlap with the one centered on Earth.
The Great Wall, sometimes specifically referred to as the CfA2 Great Wall, is an immense galaxy filament. It is one of the largest known superstructures in the observable universe.
Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors.
In astronomy, a redshift survey is a survey of a section of the sky to measure the redshift of astronomical objects: usually galaxies, but sometimes other objects such as galaxy clusters or quasars. Using Hubble's law, the redshift can be used to estimate the distance of an object from Earth. By combining redshift with angular position data, a redshift survey maps the 3D distribution of matter within a field of the sky. These observations are used to measure detailed statistical properties of the large-scale structure of the universe. In conjunction with observations of early structure in the cosmic microwave background, these results can place strong constraints on cosmological parameters such as the average matter density and the Hubble constant.
John Peter Huchra was an American astronomer and professor. He was the Vice Provost for Research Policy at Harvard University and a Professor of Astronomy at the Center for Astrophysics | Harvard & Smithsonian. He was also a former chair of the United States National Committee for the International Astronomical Union. and past president of the American Astronomical Society.
Margaret J. Geller is an American astrophysicist at the Center for Astrophysics | Harvard & Smithsonian. Her work has included pioneering maps of the nearby universe, studies of the relationship between galaxies and their environment, and the development and application of methods for measuring the distribution of matter in the universe.
The Sloan Great Wall (SGW) is a cosmic structure formed by a giant wall of galaxies. Its discovery was announced from Princeton University on October 20, 2003, by J. Richard Gott III, Mario Jurić, and their colleagues, based on data from the Sloan Digital Sky Survey.
The Pavo–Indus Supercluster is a neighboring supercluster located about 60–70 Mpc (196–228 Mly) away in the constellations of Pavo, Indus, and Telescopium. The supercluster contains three main clusters, Abell 3656, Abell 3698, and Abell 3742.
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/h to 80/h megaparsecs —with the largest found to date being the 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.
Cosmic voids are vast spaces between filaments, 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.
The Corona Borealis Supercluster is a supercluster located in the constellation Corona Borealis and the most prominent example of its kind in the Northern Celestial Hemisphere. Dense and compact compared with other superclusters, its mass has been calculated to lie somewhere between 0.6 and 12 × 1016 solar masses (M⊙). It contains the galaxy clusters Abell 2056, Abell 2061, Abell 2065 (the most massive galaxy cluster within the supercluster), Abell 2067, Abell 2079, Abell 2089, and Abell 2092. Of these, Abell 2056, 2061, 2065, 2067 and A2089 are gravitationally bound and in the process of collapsing to form a massive cluster. This entity has an estimated mass of around 1 × 1016 M⊙. If there is inter-cluster mass present, then Abell 2092 may also be involved. It has been estimated to be 100 megaparsecs (330 million light-years) wide and 40 megaparsecs (130 million light years) deep. It has a redshift of 0.07, which is equivalent to a distance of around 265.5 megaparsecs (964 million light-years).
The Taurus Void is a vast, near-empty region of space situated between the Perseus–Pisces Supercluster and the Virgo Supercluster. The Taurus void is unique because of its relatively close proximity to Earth, and because it helps to define the edge of latter's home supercluster, the Virgo Supercluster. Despite its close proximity to Earth, the Taurus Void is not well-studied because it is partially obscured by the Milky Way when viewed from Earth. In contrast to its ambiguous boundary in the section of sky obscured by the Milky Way, the Taurus Void has a very well-defined boundary with the Perseus–Pisces supercluster.
The Hyperion proto-supercluster is the largest and earliest known proto-supercluster, 5,000 times the mass of the Milky Way and seen at 20% of the current age of the universe. It was discovered in 2018 by analysing the redshifts of 10,000 objects observed with the Very Large Telescope in Chile.
