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Great Wall (astronomy)
The Great Wall (also called Coma 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. This structure was discovered c. 1989 by a team of American astronomers led by Margaret J. Geller and John Huchra while analyzing data gathered by the second CfA Redshift Survey of the Center for Astrophysics Harvard & Smithsonian (CfA). Characteristics The term "Great" has been added to distinguish it as an even larger type compared to standard galaxy walls. Great walls are so rare that only five or possibly six (if the disputed Hercules–Corona Borealis Great Wall is counted) of them have been discovered to date. The CfA2 Great Wall has the maximum dimensions of either 500 million or 750 million light years depending on the figure and the reference used. It is 200 million light years in width and about 16 million light years in thickness. Its nearest point is about 30 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coma Wall
A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhibit a complete absence of wakefulness and are unable to consciously feel, speak or move. Comas can be derived by natural causes, or can be medically induced. Clinically, a coma can be defined as the inability consistently to follow a one-step command. It can also be defined as a score of ≤ 8 on the Glasgow Coma Scale (GCS) lasting ≥ 6 hours. For a patient to maintain consciousness, the components of ''wakefulness'' and ''awareness'' must be maintained. Wakefulness describes the quantitative degree of consciousness, whereas awareness relates to the qualitative aspects of the functions mediated by the cortex, including cognitive abilities such as attention, sensory perception, explicit memory, language, the execution of tasks, temporal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Redshift Survey
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. Generally the construction of a redshift survey involves two phases: first the selected area of the sky is imaged with a wide-field telescope, then galaxies brighter than a defined limit are selected from the resulting images as n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sloan Great Wall
The Sloan Great Wall (SGW) is a cosmic structure formed by a giant wall of galaxies (a galaxy filament). 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. Size The wall measures in length, located approximately one billion light-years away. In the sky, it is located within the region of the constellations Corvus, Hydra and Centaurus. It is approximately 1/60 of the diameter of the observable universe, making it the sixth largest known object after the large quasar groups Clowes-Campusano LQG, U1.11, Huge-LQG, the Giant GRB Ring and the galaxy filament Hercules–Corona Borealis Great Wall (Her-CrB GW), respectively. The Sloan Great Wall is between 1.8–2.7 times longer than the CfA2 Great Wall of galaxies (discovered by Margaret Geller and John Huchra of Harvard in 1989). It also contains several galactic supercluster A superclus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Redshift Survey
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. Generally the construction of a redshift survey involves two phases: first the selected area of the sky is imaged with a wide-field telescope, then galaxies brighter than a defined limit are selected from the resulting images as n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Observable Universe
The observable universe is a ball-shaped region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time, because the electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. There may be 2 trillion galaxies in the observable universe, although that number was reduced in 2021 to only 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 and is unique for every unique observational position. The word ''observable'' in this sense does not refer to the capability of modern technology to detect light or other information from an object, or whether there is anything to be detected. It refers to the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cosmic String
Cosmic strings are hypothetical 1-dimensional topological defects which may have formed during a symmetry-breaking phase transition in the early universe when the topology of the vacuum manifold associated to this symmetry breaking was not simply connected. Their existence was first contemplated by the theoretical physicist Tom Kibble in the 1970s. The formation of cosmic strings is somewhat analogous to the imperfections that form between crystal grains in solidifying liquids, or the cracks that form when water freezes into ice. The phase transitions leading to the production of cosmic strings are likely to have occurred during the earliest moments of the universe's evolution, just after cosmological inflation, and are a fairly generic prediction in both quantum field theory and string theory models of the early universe. Theories containing cosmic strings In string theory, the role of cosmic strings can be played by the fundamental strings (or F-strings) themselves that defin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CMB Cold Spot
The CMB Cold Spot or WMAP Cold Spot is a region of the sky seen in microwaves that has been found to be unusually large and cold relative to the expected properties of the cosmic microwave background radiation (CMBR). The "Cold Spot" is approximately 70 µK (0.00007 K) colder than the average CMB temperature (approximately 2.7 K), whereas the root mean square of typical temperature variations is only 18 µK.After the dipole anisotropy, which is due to the Doppler shift of the microwave background radiation due to our peculiar velocity relative to the comoving cosmic rest frame, has been subtracted out. This feature is consistent with the Earth moving at some 627 km/s towards the constellation Virgo. At some points, the "cold spot" is 140 µK colder than the average CMB temperature. The radius of the "cold spot" subtends about 5°; it is centered at the galactic coordinate , (equatorial: ''α'' = , ''δ'' = ). It is, therefore, in the Souther ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Baryon
In particle physics, a baryon is a type of composite subatomic particle which contains an odd number of valence quarks (at least 3). Baryons belong to the hadron family of particles; hadrons are composed of quarks. Baryons are also classified as fermions because they have half-integer spin. The name "baryon", introduced by Abraham Pais, comes from the Greek word for "heavy" (βαρύς, ''barýs''), because, at the time of their naming, most known elementary particles had lower masses than the baryons. Each baryon has a corresponding antiparticle (antibaryon) where their corresponding antiquarks replace quarks. For example, a proton is made of two up quarks and one down quark; and its corresponding antiparticle, the antiproton, is made of two up antiquarks and one down antiquark. Because they are composed of quarks, baryons participate in the strong interaction, which is mediated by particles known as gluons. The most familiar baryons are protons and neutrons, both of which ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dark Matter
Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not absorb, reflect, or emit electromagnetic radiation and is, therefore, difficult to detect. Various astrophysical observationsincluding gravitational effects which cannot be explained by currently accepted theories of gravity unless more matter is present than can be seenimply dark matter's presence. For this reason, most experts think that dark matter is abundant in the universe and has had a strong influence on its structure and evolution. The primary evidence for dark matter comes from calculations showing that many galaxies would behave quite differently if they did not contain a large amount of unseen matter. Some galaxies would not have formed at all and others would not move as they currently do. Other lines of evidence include observa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Galaxy Filament
In cosmology, galaxy filaments (subtypes: supercluster complexes, galaxy walls, and galaxy sheets) Boris V. Komberg, Andrey V. Kravtsov, Vladimir N. Lukash; "The search and investigation of the Large Groups of Quasars" ; ;R.G. Clowes; "Large Quasar Groups - A Short Review"; ''The New Era of Wide Field Astronomy'', ASP Conference Series, vol. 232.; 2001; Astronomical Society of the Pacific; ; are the largest known structures in the universe, consisting of walls of gravitationally bound galaxy superclusters. These massive, thread-like formations can reach 80 parsec#Megaparsecs and gigaparsecs, megaparsecs ''h''−1 (or of the order of 160 to 260 million light-years) and form the boundaries between large void (astronomy), voids. Formation In the Lambda-CDM model, standard model of the evolution of the universe, galactic filaments form along and follow web-like strings of dark matter—also referred to as the galactic web or cosmic web. It is thought that this dark matter dictates ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lambda-CDM Model
The ΛCDM (Lambda cold dark matter) or Lambda-CDM model is a parameterization of the Big Bang cosmological model in which the universe contains three major components: first, a cosmological constant denoted by Lambda (Greek Λ) associated with dark energy; second, the postulated cold dark matter (abbreviated CDM); and third, ordinary matter. It is frequently referred to as the ''standard model'' of Big Bang cosmology because it is the simplest model that provides a reasonably good account of the following properties of the cosmos: * the existence and structure of the cosmic microwave background * the large-scale structure in the distribution of galaxies * the observed abundances of hydrogen (including deuterium), helium, and lithium * the accelerating expansion of the universe observed in the light from distant galaxies and supernovae The model assumes that general relativity is the correct theory of gravity on cosmological scales. It emerged in the late 1990s as a concord ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zone Of Avoidance
The Zone of Avoidance (ZOA, ZoA), or Zone of Galactic Obscuration (ZGO), is the area of the sky that is obscured by the Milky Way. The Zone of Avoidance was originally called the Zone of Few Nebulae in an 1878 paper by English astronomer Richard Proctor that referred to the distribution of "nebulae" in John Herschel's '' General Catalogue of Nebulae''.Kraan-Korteweg & Lahav 2000, p. 2 Background When viewing space from Earth, the attenuation, interstellar dust and stars in the plane of the Milky Way (the galactic plane) obstruct the view of around 20% of the extragalactic sky at visible wavelengths. As a result, optical galaxy catalogues are usually incomplete close to the galactic plane. Modern developments Many projects have attempted to bridge the gap in knowledge caused by the Zone of Avoidance. The dust and gas in the Milky Way cause extinction at optical wavelengths, and foreground stars can be confused with background galaxies. However, the effect of extinction drops at lo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
