1.
Void (astronomy)
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Cosmic voids are vast spaces between filaments, which contain very few or no galaxies. Voids typically have a diameter of 10 to 100 megaparsecs, particularly large voids and they have less than one-tenth of the average density of matter abundance that is considered typical for the observable Universe. They were first discovered in 1978 in a study by Stephen Gregory. Voids are believed to have formed by baryon acoustic oscillations in the Big Bang. Starting from initially small anisotropies from quantum fluctuations in the early Universe, regions of higher density collapsed more rapidly under gravity, eventually resulting in the large-scale, foam-like structure or “cosmic web” of voids and galaxy filaments seen today. Voids located in high-density environments are smaller than voids situated in low-density spaces of the universe, Voids appear to correlate with the observed temperature of the cosmic microwave background because of the Sachs–Wolfe effect. Colder regions correlate with voids and hotter regions correlate with filaments because of gravitational redshifting, as the Sachs–Wolfe effect is only significant if the Universe is dominated by radiation or dark energy, the existence of voids is significant in providing physical evidence for dark energy. The structure of our Universe can be broken down into components that can describe the characteristics of individual regions of the cosmos. These are the structural components of the cosmic web, Voids – vast, largely spherical regions with very low cosmic mean densities. Walls – the regions that contain the typical cosmic mean density of matter abundance, walls can be further broken down into two smaller structural features, Clusters – highly concentrated zones where walls meet and intersect, adding to the effective size of the local wall. Filaments – the branching arms of walls that can stretch for tens of megaparsecs, Voids have a mean density less than a tenth of the average density of the universe. This serves as a working definition even though there is no single definition of what constitutes a void. In the redshift surveys, the depth was calculated from the individual redshifts of the due to the expansion of the Universe according to Hubbles law. 1978 – The first two papers on the topic of voids in the scale structure were published referencing voids found in the foreground of the Coma/A1367 clusters. 1981 – Discovery of a void in the Bootes region of the sky that was nearly 50 h−1 Mpc in diameter. 1985 – Details of the supercluster and void structure of the Perseus-Pisces region were surveyed,1989 – The Center for Astrophysics Redshift Survey revealed that large voids, sharp filaments, and the walls that surround them dominate the large-scale structure of the Universe. 1991 – The Las Campanas Redshift Survey confirmed the abundance of voids in the structure of the Universe. 1995 – Comparisons of optically selected galaxy surveys indicate that the voids are found regardless of the sample selection
2.
Galaxy cluster
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They are the largest known gravitationally bound structures in the universe and 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, 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 star clusters, such as clusters, which are structures of stars within galaxies, or with globular clusters. Small aggregates of galaxies are referred to as groups of galaxies rather than clusters of galaxies, the groups and clusters can themselves cluster together to form superclusters. Notable galaxy clusters in the relatively nearby Universe include the Virgo Cluster, Fornax Cluster, Hercules Cluster, a very large aggregation of galaxies known as the Great Attractor, dominated by the Norma Cluster, is massive enough to affect the local expansion of the Universe. Notable galaxy clusters in the distant, high-redshift Universe include SPT-CL J0546-5345 and SPT-CL J2106-5844, using the Chandra X-ray Observatory, structures such as cold fronts and shock waves have also been found in many galaxy clusters. Galaxy clusters typically have the properties, They contain 100 to 1,000 galaxies, hot X-ray- emitting gas. Details are described in the Composition section, the distribution of the three components is approximately the same in the cluster. They have total masses of 1014 to 1015 solar masses and they typically have a diameter from 2 to 10 Mpc. The spread of velocities for the galaxies is about 800–1000 km/s. There are three components of a galaxy cluster. They are tabulated below, Stars, Star clusters, Galaxies, Galaxy clusters, Super clusters Abell catalogue Intracluster medium List of Abell clusters
3.
Galaxy group
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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, Groups of galaxies are the smallest aggregates of galaxies. They typically contain no more than 50 galaxies in a diameter of 1 to 2 megaparsecs and their mass is approximately 1013 solar masses. The spread of velocities for the galaxies is about 150 km/s. However, this definition should be used as a guide only, as larger, Groups are the most common structures of galaxies in the universe, comprising at least 50% of the galaxies in the local universe. Groups have a range between those of the very large elliptical galaxies and clusters of galaxies. In the local universe, about half of the groups exhibit diffuse X-ray emissions from their intracluster media and those that emit X-rays appear to have early-type galaxies as members. The diffuse X-ray emissions come from zones within the inner 10-50% of the virial radius. There are several subtypes of groups, Compact groups are small groups in closely grouped in a small area. They typically have around 5 galaxies in close proximity relatively isolated from other galaxies, the first discovered, Stephans Quintet, was discovered in 1877. Though Stephans Quintet itself is a group of 4 and a foreground galaxy. Astronomer Paul Hickson created a catalogue of such groups in 1982, Compact groups of galaxies readily show the effect of dark matter, as the visible mass is greatly less than that needed to dynamically bind the galaxies into a bound group. Compact galaxy groups are also not dynamically stable over Hubble time, fossil galaxy groups, fossil groups, or fossil clusters are believed to be the end-result of galaxy merging within a normal galaxy group, leaving behind the X-ray halo of the progenitor group. Galaxies within a group interact and merge, the physical process behind this galaxy-galaxy merger is dynamical friction. The time-scales for dynamical friction on luminous galaxies suggest that groups are old. Fossil groups are thus an important laboratory for studying the formation and evolution of galaxies, fossil groups may still contain unmerged dwarf galaxies, but the more massive members of the group have condensed into the central galaxy. The closest fossil group to the Milky Way is NGC6482, proto-groups are groups that are in the process of formation. They are the form of protoclusters
4.
Milky Way
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The Milky Way is the galaxy that contains our Solar System. The descriptive milky is derived from the appearance from Earth of the galaxy – a band of light seen in the night sky formed from stars that cannot be distinguished by the naked eye. The term Milky Way is a translation of the Latin via lactea, from Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610, until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies, the Milky Way is a barred spiral galaxy with a diameter between 100,000 light-years and 180,000 light-years. The Milky Way is estimated to contain 100–400 billion stars, there are probably at least 100 billion planets in the Milky Way. The Solar System is located within the disk, about 26,000 light-years from the Galactic Center, on the edge of one of the spiral-shaped concentrations of gas. The stars in the inner ≈10,000 light-years form a bulge, the very center is marked by an intense radio source, named Sagittarius A*, which is likely to be a supermassive black hole. Stars and gases at a range of distances from the Galactic Center orbit at approximately 220 kilometers per second. The constant rotation speed contradicts the laws of Keplerian dynamics and suggests much of the mass of the Milky Way does not emit or absorb electromagnetic radiation. This mass has been termed dark matter, the rotational period is about 240 million years at the position of the Sun. The Milky Way as a whole is moving at a velocity of approximately 600 km per second with respect to frames of reference. The oldest stars in the Milky Way are nearly as old as the Universe itself, the Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which is a component of the Virgo Supercluster, which is itself a component of the Laniakea Supercluster. The Milky Way can be seen as a band of white light some 30 degrees wide arcing across the sky. Dark regions within the band, such as the Great Rift, the area of the sky obscured by the Milky Way is called the Zone of Avoidance. The Milky Way has a low surface brightness. Its visibility can be reduced by background light such as light pollution or stray light from the Moon. The sky needs to be darker than about 20.2 magnitude per square arcsecond in order for the Milky Way to be seen and it should be visible when the limiting magnitude is approximately +5.1 or better and shows a great deal of detail at +6.1
5.
Local Group
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The Local Group is the galaxy group that includes the Milky Way. The Local Group comprises more than 54 galaxies, most of them dwarf galaxies and its gravitational center is located somewhere between the Milky Way and the Andromeda Galaxy. The Local Group covers a diameter of 10 Mly and has a binary distribution, the group itself is a part of the larger Virgo Supercluster, which in turn may be a part of the Laniakea Supercluster. The three largest members of the group are the Andromeda Galaxy, the Milky Way and the Triangulum Galaxy, the larger two of these spiral galaxies each have their own system of satellite galaxies. The Triangulum Galaxy may or may not be a companion to the Andromeda Galaxy, pisces Dwarf is equidistant from the Andromeda Galaxy and the Triangulum Galaxy, so it may be a satellite of either. The membership of NGC3109, with its companions Sextans A, the term The Local Group was introduced by Edwin Hubble in Chapter VI of his 1936 book The Realm of the Nebulae. He also identified IC10 as a possible Local Group member, by 2003, the number of known Local Group members had increased from his initial 12 to 36. Smiths Cloud, a high-velocity cloud, between 32,000 and 49,000 light years from Earth and 8,000 light years from the disk of the Milky Way galaxy HVC 127-41-330, updated Information on the Local Group. The Publications of the Astronomical Society of the Pacific
6.
Laniakea Supercluster
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The Laniakea Supercluster is the galaxy supercluster that is home to the Milky Way and approximately 100,000 other nearby galaxies. The new definition of the local supercluster subsumes the prior defined local supercluster, the Laniakea Supercluster encompasses approximately 100,000 galaxies stretched out over 160 megaparsecs. It has the mass of 1017 solar masses, or a hundred thousand times that of our galaxy. It consists of four subparts, which were previously as separate superclusters, Virgo Supercluster. The entire supercluster consists of approximately 300 to 500 known galaxy clusters, the real number may be much larger because some of these are traversing the Zone of Avoidance, making them essentially undetectable. Superclusters are some of the universes largest structures and have boundaries that are difficult to define, the team used radio telescopes to map the motions of a large collection of local galaxies. Within a given supercluster, most galaxy motions will be directed inward, toward the center of mass, unlike its constituent clusters, Laniakea is not gravitationally bound and is projected to be torn apart by dark energy. With that limitation, Laniakea is shown to be heading in the direction of the Shapley Supercluster, south African astronomer Tony Fairall stated in 1988 that redshifts suggested that the Virgo and Hydra-Centaurus Superclusters may be connected. The neighbouring superclusters to Laniakea are the Shapley Supercluster, Hercules Supercluster, Coma Supercluster, the edges of the superclusters and Laniakea were not clearly known at the time of Laniakeas definition. The name laniakea means immense heaven in Hawaiian, from lani for heaven, the name was suggested by Nawaa Napoleon, an associate professor of Hawaiian language at Kapiolani Community College. The name honors Polynesian navigators, who used knowledge of the heavens to navigate the Pacific Ocean, R. Brent Tully, Hélène Courtois, Yehuda Hoffman, Daniel Pomarède. Collective Evolution, Scientists Mapped 8000 Galaxies & Made An Amazing Discovery
7.
Hubble's law
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Hubbles law is considered the first observational basis for the expansion of the universe and today serves as one of the pieces of evidence most often cited in support of the Big Bang model. The motion of objects due solely to this expansion is known as the Hubble flow. Two years later Edwin Hubble confirmed the existence of that law, Hubble inferred the recession velocity of the objects from their redshifts, many of which were earlier measured and related to velocity by Vesto Slipher in 1917. The law is expressed by the equation v = H0D. The SI unit of H0 is s−1 but it is most frequently quoted in /Mpc, the reciprocal of H0 is the Hubble time. Applying the most general principles to the nature of the universe yielded a solution that conflicted with the then-prevailing notion of a static universe. In 1922, Alexander Friedmann derived his Friedmann equations from Einsteins field equations, the parameter used by Friedmann is known today as the scale factor which can be considered as a scale invariant form of the proportionality constant of Hubbles law. Georges Lemaître independently found a solution in 1927. The Friedmann equations are derived by inserting the metric for a homogeneous and isotropic universe into Einsteins field equations for a fluid with a given density and this idea of an expanding spacetime would eventually lead to the Big Bang and Steady State theories of cosmology. In 1927, two years before Hubble published his own article, the Belgian priest and astronomer Georges Lemaître was the first to publish research deriving what is now known as Hubbles Law. According to the Canadian astronomer Sidney van den Bergh, The 1927 discovery of the expansion of the Universe by Lemaitre was published in French in a low-impact journal. In the 1931 high-impact English translation of this article a critical equation was changed by omitting reference to what is now known as the Hubble constant and it is now known that the alterations in the translated paper were carried out by Lemaitre himself. Before the advent of modern cosmology, there was talk about the size. In 1920, the famous Shapley-Curtis debate took place between Harlow Shapley and Heber D. Curtis over this issue, Shapley argued for a small universe the size of the Milky Way galaxy and Curtis argued that the Universe was much larger. The issue was resolved in the decade with Hubbles improved observations. Edwin Hubble did most of his professional astronomical observing work at Mount Wilson Observatory and his observations of Cepheid variable stars in spiral nebulae enabled him to calculate the distances to these objects. Surprisingly, these objects were discovered to be at distances which placed them well outside the Milky Way and they continued to be called nebulae and it was only gradually that the term galaxies took over. The parameters that appear in Hubble’s law, velocities and distances, are not directly measured, in reality we determine, say, a supernova brightness, which provides information about its distance, and the redshift z = ∆λ/λ of its spectrum of radiation
8.
Virgo Supercluster
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At least 100 galaxy groups and clusters are located within its diameter of 33 megaparsecs. It is one of about 10 million superclusters in the observable universe, a 2014 study indicates that the Virgo Supercluster is only a lobe of a greater supercluster, Laniakea, which is centered on the Great Attractor. Beginning with the first large sample of published by William and John Herschel in 1863. Debate went on during the 1960s and 1970s as to whether the Local Supercluster was actually a structure or an alignment of galaxies. The issue was resolved with the redshift surveys of the late 1970s and early 1980s. In a comprehensive 1982 paper, R. Brent Tully presented the conclusions of his research concerning the structure of the LS. It consists of two components, a flattened disk containing two-thirds of the superclusters luminous galaxies, and a roughly spherical halo containing the remaining one-third. The disk itself is an ellipsoid with a long axis / short axis ratio of at least 6 to 1. Data released in June 2003 from the 5-year Two-degree-Field Galaxy Redshift Survey has allowed astronomers to compare the LS to other superclusters, the LS represents a typical poor supercluster of rather small size. It has one rich galaxy cluster in the center, surrounded by filaments of galaxies, the Local Group is located on the outskirts of the LS in a small filament extending from the Fornax Cluster to the Virgo Cluster. The Virgo Superclusters volume is very approximately 7000 times that of the Local Group or 100 billion times that of the Milky Way, see volumes of similar orders of magnitude. The number density of galaxies in the LS falls off with the square of the distance from its center near the Virgo Cluster, overall, the vast majority of the luminous galaxies are concentrated in a small number of clouds. Ninety-eight percent can be found in the following 11 clouds, Canes Venatici, Virgo Cluster, Virgo II, Leo II, Virgo III, Crater, Leo I, Leo Minor, Draco, Antlia and NGC5643. The luminous galaxies in the halo are also concentrated in a number of clouds. This distribution indicates that most of the volume of the plane is a great void. A helpful analogy that matches the distribution is that of soap bubbles. Flattish clusters and superclusters are found at the intersection of bubbles, long filamentary structures seem to predominate. An example of this is the Hydra-Centaurus Supercluster, the nearest supercluster to the LS, lynden-Bell et al. dubbed the cause of this the Great Attractor
9.
Great Attractor
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This mass is observable by its effect on the motion of galaxies and their associated clusters over a region hundreds of millions of light-years across. The Great Attractor is moving towards the Shapley Supercluster, the variations in their redshifts are known as peculiar velocities, and cover a range from about +700 km/s to −700 km/s, depending on the angular deviation from the direction to the Great Attractor. The first indications of a deviation from uniform expansion of the universe were reported in 1973, in 1992, much of the apparent signal of the Great Attractor was attributed to the effect of Malmquist bias. Dark flow is a term that describes a possible non-random component of the peculiar velocity of galaxy clusters. The measured velocity is the sum of that predicted by Hubbles Law added to a small, unexplained. The proposed Laniakea Supercluster is defined as the Great Attractors basin, encompassing the former superclusters of Virgo, thus the Great Attractor would be the core of the new supercluster. Dipole repeller CfA2 Great Wall Dark Matter Hercules–Corona Borealis Great Wall Shapley Supercluster Dressler, voyage to the Great Attractor, Exploring Intergalactic Space. New Map Locates Milky Way in Neighborhood of 100,000 Galaxies, nadia Drake, for National Geographic,3 September 2014 Cosmography of the Local Universe at Vimeo showing the Great Attractor
10.
Redshift
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In physics, redshift happens when light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum. Some redshifts are an example of the Doppler effect, familiar in the change of apparent pitches of sirens, a redshift occurs whenever a light source moves away from an observer. Finally, gravitational redshift is an effect observed in electromagnetic radiation moving out of gravitational fields. However, redshift is a common term and sometimes blueshift is referred to as negative redshift. Knowledge of redshifts and blueshifts has been applied to develop several terrestrial technologies such as Doppler radar and radar guns, Redshifts are also seen in the spectroscopic observations of astronomical objects. Its value is represented by the letter z, a special relativistic redshift formula can be used to calculate the redshift of a nearby object when spacetime is flat. However, in contexts, such as black holes and Big Bang cosmology. Special relativistic, gravitational, and cosmological redshifts can be understood under the umbrella of frame transformation laws, the history of the subject began with the development in the 19th century of wave mechanics and the exploration of phenomena associated with the Doppler effect. The effect is named after Christian Doppler, who offered the first known physical explanation for the phenomenon in 1842, the hypothesis was tested and confirmed for sound waves by the Dutch scientist Christophorus Buys Ballot in 1845. Doppler correctly predicted that the phenomenon should apply to all waves, before this was verified, however, it was found that stellar colors were primarily due to a stars temperature, not motion. Only later was Doppler vindicated by verified redshift observations, the first Doppler redshift was described by French physicist Hippolyte Fizeau in 1848, who pointed to the shift in spectral lines seen in stars as being due to the Doppler effect. The effect is called the Doppler–Fizeau effect. In 1868, British astronomer William Huggins was the first to determine the velocity of a moving away from the Earth by this method. In 1871, optical redshift was confirmed when the phenomenon was observed in Fraunhofer lines using solar rotation, about 0.1 Å in the red. In 1887, Vogel and Scheiner discovered the annual Doppler effect, in 1901, Aristarkh Belopolsky verified optical redshift in the laboratory using a system of rotating mirrors. The word does not appear unhyphenated until about 1934 by Willem de Sitter, perhaps indicating that up to point its German equivalent. Beginning with observations in 1912, Vesto Slipher discovered that most spiral galaxies, Slipher first reports on his measurement in the inaugural volume of the Lowell Observatory Bulletin. Three years later, he wrote a review in the journal Popular Astronomy, Slipher reported the velocities for 15 spiral nebulae spread across the entire celestial sphere, all but three having observable positive velocities
11.
George O. Abell
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George Ogden Abell was an astronomer at UCLA. He worked as an astronomer, teacher, administrator, popularizer of science and education. Abell received his B. S. M. S. and he began his astronomical career as a tour guide at the Griffith Observatory in Los Angeles. His best known work was his catalogue of clusters of galaxies collected during the Palomar Sky Survey and he analyzed their formation and evolution. He demonstrated that second-order clustering existed, disproving the hierarchical model of Carl Charlier and he also discovered how cluster luminosity could be used as a distance scale. He also collated a famous list of 86 planetary nebulae in 1966 which includes Abell 39, the Abell catalogue is an almost complete list of approximately 4,000 clusters containing at least thirty members up to a redshift of z =0.2. The original catalogue of clusters in the hemisphere was published in 1958. The extended catalogue, including clusters in the hemisphere, was published posthumously in 1989 in collaboration with Harold G. Corwin. Abell also co-discovered periodic comet 52P/Harrington-Abell, together with Peter Goldreich, he correctly determined that planetary nebulae evolve from red giants. Abell was passionate about educating people, serving for over twenty years as a faculty member at the Summer Science Program for high school students. The program memorializes him with its Abell Scholarship Fund and he was involved in the production of the educational TV series Understanding Space and Time and Project Universe. Abell was also passionate about debunking pseudoscientific claims such as those by Immanuel Velikovsky and he was a co-founder of the Committee on Scientific Investigation of Claims of the Paranormal and contributed articles to their journal, The Skeptical Inquirer. Abell served as president of the Cosmology Commission of the International Astronomical Union and as president and he was elected a fellow of the Royal Astronomical Society in 1970. He was chairman of the UCLA Astronomy Department from 1968 to 1975, at the time of his death, he was to have become editor of the Astronomical Journal effective January 1,1984. Asteroid 3449 Abell is named in his honor, as is The George Abell Observatory at the Open University in Milton Keynes, England. O. Exploration of the Universe, Saunders College Pub, 6th/Rev edition ISBN 0-03-094666-2 Abell, G. O. Wolff, S. C. and Morrison, D. Realm of the Universe, Saunders College Publishing, 5th ed.1994 edition ISBN 0-03-001664-9 Abell, George O, Singer, Barry, Science and the Paranormal, Probing the Existence of the Supernatural. A catalog of rich clusters of galaxies, American Astronomical Society ASIN B000726Y06
12.
Abell catalogue
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The Abell catalog of rich clusters of galaxies is an all-sky catalog of 4,073 rich galaxy clusters of nominal redshift z ≤0.2. The Abell catalog, and especially its clusters, are of interest to astronomers as challenge objects to be viewed in dark locations on large aperture amateur telescopes. The original catalog of 2,712 rich clusters of galaxies was published in 1958 by George O. Abell, a. G. Wilson, another of the principal observers, assisted Abell in the initial stages of the survey by routinely inspecting the plates as they were produced. After the completion of the survey, Abell went over the plates again, in both cases inspection was made with a 3. 5× magnifying lens. To qualify for inclusion in the catalog, a cluster had to satisfy four criteria, Richness, to ensure a healthy margin or error, this criterion was not applied rigorously, and the final catalog included many clusters with fewer than fifty members. The precise value of the Abell radius depends on the value taken for that parameter h, for h =0.75, the Abell radius is 2 megaparsecs. This is more than twice the estimate Abell gave in 1958, distance, A cluster should have a nominal redshift of between 0.02 and 0.2. It has since been shown many of the clusters in the catalog are more remote even than this. In the catalog as originally published the clusters were listed in increasing order of right ascension, equatorial coordinates were given for the equinox of 1855 and galactic coordinates for 1900. The Southern Survey added a further 1,361 rich clusters to Abell’s original Northern Survey, the deep IIIa-J plates of the Southern Sky Survey were used in the survey. These photographic plates were taken with the United Kingdom’s 1. 2-metre Schmidt Telescope at Siding Spring Observatory, Australia, Abell began the survey during a sabbatical year in Edinburgh in 1976. By then about half the survey had been completed, as before, clusters were included if they had at least thirty bright galaxies, as it was estimated that this would all but eliminate the possibility of genuinely rich clusters being omitted. The Southern Survey retains the system of designation devised by Abell for his original catalog, the equatorial co-ordinates are for the equinoxes 1950 and 2000, while the galactic co-ordinates are calculated from the 1950 equatorial co-ordinates. The standard format used to refer to Abell clusters is, Abell X, alternative formats include, ABCG1656, AC1656, ACO1656, A1656, and A1656.1 are not genuine rich clusters but, rather, the result of the superposition of sparser groupings. Interestingly, the large and extremely rich Virgo Cluster was excluded from the Abell catalog because it covered too large an area of the sky to appear on a single photographic plate. Catalogue of Galaxies and Clusters of Galaxies Hickson Compact Group List of Abell clusters List of galaxy clusters Abell, G O, Corwin, H G, Olowin, a Catalog of Rich Clusters of Galaxies. The Astrophysical Journal Supplement Series,70, abells 1958 paper and catalog Abell, Corwin and Olowins 1989 paper and catalog Electronic form of the Abell catalog
13.
Galaxy filament
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In physical cosmology, galaxy filaments are the largest known structures in the universe. They are massive, thread-like formations, with a length of 50 to 80 megaparsecs h−1 that form the boundaries between large voids in the universe. Filaments consist of gravitationally bound galaxies, parts wherein many galaxies are very close to one another are called superclusters. In the standard model of the evolution of the universe, galactic filaments form along and it is thought that this dark matter dictates the structure of the Universe on the grandest of scales. Dark matter gravitationally attracts baryonic matter, and it is this matter that astronomers see forming long. Discovery of structures larger than superclusters began in the late-1980s, in 1987, astronomer R. Brent Tully of the University of Hawaiis Institute of Astronomy identified what he called the Pisces–Cetus Supercluster Complex. In 1989, the CfA2 Great Wall was discovered, followed by the Sloan Great Wall in 2003, filament subtype of filaments have roughly similar major and minor axes in cross-section, along the lengthwise axis. A short filament, detected by identifying an alignment of star-forming galaxies, in the neighborhood of the Milky Way and the Local Group was proposed by Adi Zitrin and Noah Brosch. The reality of this filament, and the identification of a similar, the galaxy wall subtype of filaments have a significantly greater major axis than minor axis in cross-section, along the lengthwise axis. A wall was proposed to be the embodiment of the Great Attractor. It is sometimes referred to as the Great Attractor Wall or Norma Wall and this suggestion was superseded by the proposal of a supercluster, Laniakea, that would encompass the Great Attractor, Virgo Supercluster, Hydra-Centaurus Superclusters. A wall was proposed in 2000 to lie at z=1.47 in the vicinity of radio galaxy B3 0003+387, a wall was proposed in 2000 to lie at z=0.559 in the northern Hubble Deep Field. Large quasar groups are some of the largest structures known and they are theorized to be protohyperclusters/proto-supercluster-complexes/galaxy filament precursors. Kevin A. Pimbblet, Pulling Out Threads from the Cosmic Tapestry, pictures of the filamentary network The Universe Within One Billion Light Years with List of Nearby Superclusters
14.
Observable universe
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There are at least two trillion galaxies in the observable universe, containing more stars than all the grains of sand on planet Earth. Assuming the universe is isotropic, the distance to the edge of the universe is roughly the same in every direction. That is, the universe is a spherical volume centered on the observer. Every location in the Universe has its own universe, which may or may not overlap with the one centered on Earth. The word observable used in this sense does not depend on modern technology actually permits detection of radiation from an object in this region. It simply indicates that it is possible in principle for light or other signals from the object to reach an observer on Earth, in practice, we can see light only from as far back as the time of photon decoupling in the recombination epoch. That is when particles were first able to emit photons that were not quickly re-absorbed by other particles, before then, the Universe was filled with a plasma that was opaque to photons. The detection of gravitational waves indicates there is now a possibility of detecting signals from before the recombination epoch. The surface of last scattering is the collection of points in space at the distance that photons from the time of photon decoupling just reach us today. These are the photons we detect today as cosmic microwave background radiation, however, with future technology, it may be possible to observe the still older relic neutrino background, or even more distant events via gravitational waves. It is estimated that the diameter of the universe is about 28.5 gigaparsecs. The total mass of matter in the universe can be calculated using the critical density. Some parts of the Universe are too far away for the light emitted since the Big Bang to have had time to reach Earth. In the future, light from distant galaxies will have had time to travel. This fact can be used to define a type of cosmic event horizon whose distance from the Earth changes over time, both popular and professional research articles in cosmology often use the term universe to mean observable universe. It is plausible that the galaxies within our observable universe represent only a fraction of the galaxies in the Universe. If the Universe is finite but unbounded, it is possible that the Universe is smaller than the observable universe. In this case, what we take to be very distant galaxies may actually be duplicate images of nearby galaxies and it is difficult to test this hypothesis experimentally because different images of a galaxy would show different eras in its history, and consequently might appear quite different
15.
Galaxy groups and clusters
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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 structure of the Universe. In models for the formation of structure with cold dark matter. 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 of galaxies are the smallest aggregates of galaxies. They typically contain no more than 50 galaxies in a diameter of 1 to 2 megaparsecs and their mass is approximately 1013 solar masses. The spread of velocities for the galaxies is about 150 km/s. However, this definition should be used as a guide only, as larger, groups are the most common structures of galaxies in the universe, comprising at least 50% of the galaxies in the local universe. Groups have a range between those of the very large elliptical galaxies and clusters of galaxies. Our own Galaxy, the Milky Way, is contained in the Local Group of more than 40 galaxies, Clusters are larger than groups, although there is no sharp dividing line between the two. When observed visually, clusters appear to be collections of galaxies held together by mutual gravitational attraction, X-ray studies have revealed the presence of large amounts of intergalactic gas known as the intracluster medium. This gas is hot, between 107K and 108K, and hence emits X-rays in the form of bremsstrahlung and atomic line emission. The total mass of the gas is greater than that of the galaxies by roughly a factor of two, however, this is still not enough mass to keep the galaxies in the cluster. Since this gas is in hydrostatic equilibrium with the overall cluster gravitational field. It turns out the total mass deduced from this measurement is approximately six times larger than the mass of the galaxies or the hot gas, the missing component is known as dark matter and its nature is unknown. In a typical cluster perhaps only 5% of the mass is in the form of galaxies, maybe 10% in the form of hot X-ray emitting gas. Brownstein and Moffat use a theory of modified gravity to explain X-ray cluster masses without dark matter, Galaxy clusters are found by optical or infrared telescopes by searching for overdensities, and then confirmed by finding several galaxies at a similar redshift. Infrared searches are more useful for finding more distant clusters, X-ray, The hot plasma emits X-rays that can be detected by X-ray telescopes
16.
Virgo Cluster
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The Virgo Cluster is a cluster of galaxies whose center is 53.8 ±0.3 Mly away in the constellation Virgo. Comprising approximately 1300 member galaxies, the forms the heart of the larger Virgo Supercluster. However, the Local Group experiences the mass of the Virgo Supercluster as the Virgocentric flow and it is estimated that the Virgo Clusters mass is 1. 2×1015 M☉ out to 8 degrees of the clusters center or a radius of about 2.2 Mpc. Described by Messier as nebulae without stars, their nature was not recognized until the 1920s. The cluster subtends an arc of approximately 8 degrees centered in the constellation Virgo. Many of the galaxies of the cluster are visible with a small telescope. Its brightest member is the elliptical galaxy Messier 49, however its most famous member is the elliptical galaxy Messier 87. The cluster is a heterogeneous mixture of spirals and ellipticals. The elliptical galaxies are more concentrated than the spiral galaxies. This strongly suggests the Virgo cluster is a young cluster that is still forming. Other two nearby aggregations known as M Cloud, W Cloud, and W Cloud seem to be background systems independent of the main cluster. The large mass of the cluster is indicated by the peculiar velocities of many of its galaxies, sometimes as high as 1,600 km/s with respect to the clusters center. The Virgo cluster lies within the Virgo Supercluster, and its gravitational effect slows down the nearby galaxies, the large mass of the cluster has the effect of slowing down the recession of the Local Group from the cluster by approximately ten percent. As with many other galaxy clusters, Virgos intracluster medium is filled with a hot. Below is given a table of bright or notable objects in the Virgo Cluster, note that in some cases a galaxy may be considered in one subunit or in another Column 1, The name of the galaxy. Column 2, The right ascension for epoch 2000, Column 3, The declination for epoch 2000. Column 4, The blue apparent magnitude of the galaxy, Column 5, The galaxy type, E=Elliptical, S0=Lenticular, Sa, Sb, Sc, Sd=Spiral, SBa, SBb, SBc, SBd=Barred spiral, Sm, SBm, Irr=Irregular. Column 6, The angular diameter of the galaxy, Column 7, The diameter of the galaxy
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Galaxy
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A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. The word galaxy is derived from the Greek galaxias, literally milky, Galaxies range in size from dwarfs with just a few billion stars to giants with one hundred trillion stars, each orbiting its galaxys center of mass. Galaxies are categorized according to their morphology as elliptical, spiral. Many galaxies are thought to have holes at their active centers. The Milky Ways central black hole, known as Sagittarius A*, has a four million times greater than the Sun. Recent estimates of the number of galaxies in the observable universe range from 200 billion to 2 trillion or more, most of the galaxies are 1,000 to 100,000 parsecs in diameter and separated by distances on the order of millions of parsecs. The space between galaxies is filled with a gas having an average density of less than one atom per cubic meter. The majority of galaxies are organized into groups, clusters. At the largest scale, these associations are generally arranged into sheets and filaments surrounded by immense voids. In Greek mythology, Zeus places his son born by a mortal woman, the infant Heracles, on Heras breast while she is asleep so that the baby will drink her divine milk and will thus become immortal. Hera wakes up while breastfeeding and then realizes she is nursing a baby, she pushes the baby away, some of her milk spills and. In the astronomical literature, the capitalized word Galaxy is often used to refer to our galaxy, the Milky Way, to distinguish it from the other galaxies in our universe. The English term Milky Way can be traced back to a story by Chaucer c. 1380, See yonder, lo, the Galaxyë Which men clepeth the Milky Wey, For hit is whyt. However, the word Universe was later understood to mean the entirety of existence, so this expression fell into disuse and the objects instead became known as galaxies. Tens of thousands of galaxies have been catalogued, but only a few have well-established names, such as the Andromeda Galaxy, the Magellanic Clouds, the Whirlpool Galaxy, and the Sombrero Galaxy. Astronomers work with numbers from certain catalogues, such as the Messier catalogue, the NGC, the IC, the CGCG, all of the well-known galaxies appear in one or more of these catalogues but each time under a different number. For example, Messier 109 is a galaxy having the number 109 in the catalogue of Messier, but also codes NGC3992, UGC6937, CGCG 269-023, MCG +09-20-044. One of the arguments to do so is that these impressive objects deserve better than uninspired codes, for instance, Bodifee and Berger propose the informal, descriptive name Callimorphus Ursae Majoris for the well-formed barred galaxy Messier 109 in Ursa Major
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Fornax Cluster
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The Fornax Cluster is a cluster of galaxies lying at a distance of 62 million light-years. It is the second richest galaxy cluster within 100 million light-years and it lies primarily in the constellation Fornax, and may be associated with the nearby Eridanus Group. At the centre of the cluster lies NGC1399, other cluster members include NGC1316, NGC1365, NGC 1427A, and NGC1404. As with many other galaxy clusters, Fornax intracluster medium is filled with a hot, rarefied gas that emits X-rays. and contains a number of intergalactic stars, some of which have produced novae
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Coma Supercluster
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The Coma Supercluster is a nearby supercluster of galaxies comprising the Coma Cluster and the Leo Cluster. Located 300 million light-years from Earth, it is in the center of the Great Wall, the Coma Supercluster is the nearest massive cluster of galaxies to our own Virgo Supercluster. It is roughly spherical, about 20 million light-years in diameter and it is located in the constellation Coma Berenices. Being one of the first superclusters to be discovered, the Coma Supercluster helped astronomers understand the scale structure of the universe. Abell catalogue Large-scale structure of the universe List of Abell clusters Supercluster
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Quasar
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A quasar is an active galactic nucleus of very high luminosity. A quasar consists of a black hole surrounded by an orbiting accretion disk of gas. As gas in the accretion disk falls toward the black hole, quasars emit energy across the electromagnetic spectrum and can be observed at radio, infrared, visible, ultraviolet, and X-ray wavelengths. The most powerful quasars have luminosities exceeding 1041 W, thousands of greater than the luminosity of a large galaxy such as the Milky Way. Quasars are found over a broad range of distances. The peak epoch of quasar activity in the Universe corresponds to redshifts around 2, as of 2011, the most distant known quasar is at redshift z=7.085, light observed from this quasar was emitted when the Universe was only 770 million years old. Because quasars are distant objects, any light which reaches the Earth is redshifted due to the expansion of space. In early optical images, quasars appeared as point sources, indistinguishable from stars, with infrared telescopes and the Hubble Space Telescope, the host galaxies surrounding the quasars have been detected in some cases. These galaxies are normally too dim to be seen against the glare of the quasar, most quasars, with the exception of 3C273 whose average apparent magnitude is 12.9, cannot be seen with small telescopes. The luminosity of some quasars changes rapidly in the optical range, because these changes occur very rapidly they define an upper limit on the volume of a quasar, quasars are not much larger than the Solar System. This implies a high power density. The mechanism of brightness changes probably involves relativistic beaming of astrophysical jets pointed nearly directly toward Earth, the highest redshift quasar known is ULAS J1120+0641, with a redshift of 7.085, which corresponds to a comoving distance of approximately 29 billion light-years from Earth. Since light cannot escape the black holes, the energy is actually generated outside the event horizon by gravitational stresses. Central masses of 105 to 109 solar masses have been measured in quasars by using reverberation mapping. The matter accreting onto the hole is unlikely to fall directly in. Quasars may also be ignited or re-ignited when normal galaxies merge, in fact, it has been suggested that a quasar could form as the Andromeda Galaxy collides with our own Milky Way galaxy in approximately 3–5 billion years. More than 200,000 quasars are known, most from the Sloan Digital Sky Survey, all observed quasar spectra have redshifts between 0.056 and 7.085. Applying Hubbles law to these redshifts, it can be shown that they are between 600 million and 28.85 billion light-years away
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Illustris project
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The Illustris project is an ongoing series of astrophysical simulations run by an international collaboration of scientists. The aim is to study the processes of formation and evolution in the universe with a comprehensive physical model. Early results are described in a number of publications following widespread press coverage, the project publicly released all data produced by the simulations in April,2015. The Illustris project includes large-scale cosmological simulations of the evolution of the universe, spanning initial conditions of the Big Bang, the simulation includes many physical processes which are thought to be critical for galaxy formation. Images, videos, and other visualizations for public distribution are available at official media page. A total of 19 million CPU hours was required, using 8,192 CPU cores, the peak memory usage was approximately 25 TB of RAM. A total of 136 snapshots were saved over the course of the simulation, a code called Arepo was used to run the Illustris simulations. It was written by Volker Springel, the author as the GADGET code. The name is derived from the Sator Square and this code solves the coupled equations of gravity and hydrodynamics using a discretization of space based on a moving Voronoi tessellation. It is optimized for running on large, distributed memory supercomputers using a MPI approach, in April,2015 the project team publicly released all data products from all simulations. All original data files can be downloaded through the data release webpage. In addition to direct data download, a web-based API allows for many common search, official website Press release - Harvard-Smithsonian Center for Astrophysics. Video - Illustris Simulation - Illustris-Project. ]On YouTube Video - Search for Life in the Universe - NASA ] on YouTube
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Astrophysics and Space Science
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Astrophysics and Space Science is a bimonthly peer-reviewed scientific journal covering astronomy, astrophysics, and space science and astrophysical aspects of astrobiology. It was established in 1968 and is published by Springer Science+Business Media, the editor-in-chief is Michael A. Dopita. The journal is abtracted and indexed in the databases, According to the Journal Citation Reports
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ArXiv
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In many fields of mathematics and physics, almost all scientific papers are self-archived on the arXiv repository. Begun on August 14,1991, arXiv. org passed the half-million article milestone on October 3,2008, by 2014 the submission rate had grown to more than 8,000 per month. The arXiv was made possible by the low-bandwidth TeX file format, around 1990, Joanne Cohn began emailing physics preprints to colleagues as TeX files, but the number of papers being sent soon filled mailboxes to capacity. Additional modes of access were added, FTP in 1991, Gopher in 1992. The term e-print was quickly adopted to describe the articles and its original domain name was xxx. lanl. gov. Due to LANLs lack of interest in the rapidly expanding technology, in 1999 Ginsparg changed institutions to Cornell University and it is now hosted principally by Cornell, with 8 mirrors around the world. Its existence was one of the factors that led to the current movement in scientific publishing known as open access. Mathematicians and scientists regularly upload their papers to arXiv. org for worldwide access, Ginsparg was awarded a MacArthur Fellowship in 2002 for his establishment of arXiv. The annual budget for arXiv is approximately $826,000 for 2013 to 2017, funded jointly by Cornell University Library, annual donations were envisaged to vary in size between $2,300 to $4,000, based on each institution’s usage. As of 14 January 2014,174 institutions have pledged support for the period 2013–2017 on this basis, in September 2011, Cornell University Library took overall administrative and financial responsibility for arXivs operation and development. Ginsparg was quoted in the Chronicle of Higher Education as saying it was supposed to be a three-hour tour, however, Ginsparg remains on the arXiv Scientific Advisory Board and on the arXiv Physics Advisory Committee. The lists of moderators for many sections of the arXiv are publicly available, additionally, an endorsement system was introduced in 2004 as part of an effort to ensure content that is relevant and of interest to current research in the specified disciplines. Under the system, for categories that use it, an author must be endorsed by an established arXiv author before being allowed to submit papers to those categories. Endorsers are not asked to review the paper for errors, new authors from recognized academic institutions generally receive automatic endorsement, which in practice means that they do not need to deal with the endorsement system at all. However, the endorsement system has attracted criticism for allegedly restricting scientific inquiry, perelman appears content to forgo the traditional peer-reviewed journal process, stating, If anybody is interested in my way of solving the problem, its all there – let them go and read about it. The arXiv generally re-classifies these works, e. g. in General mathematics, papers can be submitted in any of several formats, including LaTeX, and PDF printed from a word processor other than TeX or LaTeX. The submission is rejected by the software if generating the final PDF file fails, if any image file is too large. ArXiv now allows one to store and modify an incomplete submission, the time stamp on the article is set when the submission is finalized
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PubMed Identifier
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PubMed is a free search engine accessing primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics. The United States National Library of Medicine at the National Institutes of Health maintains the database as part of the Entrez system of information retrieval, from 1971 to 1997, MEDLINE online access to the MEDLARS Online computerized database primarily had been through institutional facilities, such as university libraries. PubMed, first released in January 1996, ushered in the era of private, free, home-, the PubMed system was offered free to the public in June 1997, when MEDLINE searches via the Web were demonstrated, in a ceremony, by Vice President Al Gore. Information about the journals indexed in MEDLINE, and available through PubMed, is found in the NLM Catalog. As of 5 January 2017, PubMed has more than 26.8 million records going back to 1966, selectively to the year 1865, and very selectively to 1809, about 500,000 new records are added each year. As of the date,13.1 million of PubMeds records are listed with their abstracts. In 2016, NLM changed the system so that publishers will be able to directly correct typos. Simple searches on PubMed can be carried out by entering key aspects of a subject into PubMeds search window, when a journal article is indexed, numerous article parameters are extracted and stored as structured information. Such parameters are, Article Type, Secondary identifiers, Language, publication type parameter enables many special features. As these clinical girish can generate small sets of robust studies with considerable precision, since July 2005, the MEDLINE article indexing process extracts important identifiers from the article abstract and puts those in a field called Secondary Identifier. The secondary identifier field is to store numbers to various databases of molecular sequence data, gene expression or chemical compounds. For clinical trials, PubMed extracts trial IDs for the two largest trial registries, ClinicalTrials. gov and the International Standard Randomized Controlled Trial Number Register, a reference which is judged particularly relevant can be marked and related articles can be identified. If relevant, several studies can be selected and related articles to all of them can be generated using the Find related data option, the related articles are then listed in order of relatedness. To create these lists of related articles, PubMed compares words from the title and abstract of each citation, as well as the MeSH headings assigned, using a powerful word-weighted algorithm. The related articles function has been judged to be so precise that some researchers suggest it can be used instead of a full search, a strong feature of PubMed is its ability to automatically link to MeSH terms and subheadings. Examples would be, bad breath links to halitosis, heart attack to myocardial infarction, where appropriate, these MeSH terms are automatically expanded, that is, include more specific terms. Terms like nursing are automatically linked to Nursing or Nursing and this important feature makes PubMed searches automatically more sensitive and avoids false-negative hits by compensating for the diversity of medical terminology. The My NCBI area can be accessed from any computer with web-access, an earlier version of My NCBI was called PubMed Cubby
. Bibcode:2006Ap&SS.302...43H. doi:10.1007/s10509-005-9006-7.
Media related to Superclusters of galaxies at Wikimedia Commons
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