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.
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
8.
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
9.
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
10.
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
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