The Virgo Cluster is a cluster of galaxies whose center is 53.8 ± 0.3 Mly away in the constellation Virgo. Comprising 1300 member galaxies, the cluster forms the heart of the larger Virgo Supercluster, of which the Local Group is a member; the Local Group experiences the mass of the Virgo Supercluster as the Virgocentric flow. It is estimated that the Virgo Cluster's mass is 1.2×1015 M☉ out to 8 degrees of the cluster's center or a radius of about 2.2 Mpc. Many of the brighter galaxies in this cluster, including the giant elliptical galaxy Messier 87, were discovered in the late 1770s and early 1780s and subsequently included in Charles Messier's catalogue of non-cometary fuzzy objects. Described by Messier as nebulae without stars, their true nature was not recognized until the 1920s; the cluster subtends a maximum arc of 8 degrees centered in the constellation Virgo. Although some of the cluster's most prominent members can be seen with smaller instruments, a 6-inch telescope will reveal about 160 of the cluster's galaxies on a clear night.
Its brightest member is the elliptical galaxy Messier 49. The cluster is a heterogeneous mixture of spirals and ellipticals; as of 2004, it is believed that the spiral galaxies of the cluster are distributed in an oblong prolate filament four times as long as it is wide, stretching along the line of sight from the Milky Way. The elliptical galaxies are more centrally concentrated than the spiral galaxies; the cluster is an aggregrate of at least three separate subclumps: Virgo A, centered on M87, a second centered on the galaxy M86, Virgo B, centered on M49, with some authors including a Virgo C subcluster, centered on the galaxy M60 as well as a LVC subclump, centered on the large spiral galaxy NGC 4216. Of all of the subclumps, Virgo A, formed by a mixture of elliptical and gas-poor spiral galaxies, is the dominant one, with a mass of 1014 M☉, an order of magnitude larger than the other two subclumps; the three subgroups are in the process of merging to form a larger single cluster and are surrounded by other smaller galaxy clouds composed of spiral galaxies, known as N Cloud, S Cloud, Virgo E that are in the process of infalling to merge with them, plus other farther isolated galaxies and galaxy groups that are attracted by the gravity of Virgo to merge with it in the future.
This suggests the Virgo cluster is a dynamically young cluster, still forming. Other two nearby aggregations known as M Cloud, W Cloud, W' Cloud seem to be background systems independent of the main cluster; the large mass of the cluster is indicated by the high peculiar velocities of many of its galaxies, sometimes as high as 1,600 km/s with respect to the cluster's center. The Virgo cluster lies within the Virgo Supercluster, 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 ten percent. As with many other rich galaxy clusters, Virgo's intracluster medium is filled with a hot, rarefied plasma at temperatures of 30 million kelvins that emits X-Rays. Within the intracluster medium are found a large number of intergalactic stars, including some planetary nebulae, it is theorized that these were expelled from their home galaxies by interactions with other galaxies. The ICM contains some globular clusters stripped off dwarf galaxies, at least one star formation region.
Below is given a table of bright or notable objects in the Virgo Cluster and the subunit of the cluster in which they are located. Note that in some cases a galaxy may be considered in a different subunit by other researchers 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. Column 8: The recessional velocity of the galaxy relative to the cosmic microwave background. Column 9: Subcluster where the galaxy is located. Fainter galaxies within the cluster are known by their numbers in the Virgo Cluster Catalog members of the numerous dwarf galaxy population. Coma Cluster – another large, nearby cluster of galaxies Eridanus Cluster Fornax Cluster – a smaller nearby cluster of galaxies Norma Cluster List of galaxy clusters Virgocentric flow The Virgo Cluster at An Atlas of the Universe, map of the 160 largest galaxies California Institute of Technology site on Virgo cluster.
The Virgo Cluster of Galaxies, SEDS Messier pages Partial Virgo cluster centered on M87 The Virgo Cluster Catalog
Galaxy groups and clusters
Galaxy groups and clusters are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation. They form the densest part of the large-scale structure of the Universe. In models for the gravitational formation of structure with cold dark matter, the smallest structures collapse first and build the largest structures, clusters of galaxies. Clusters are formed recently between 10 billion years ago and now. Groups and clusters may contain ten to thousands of individual galaxies; the clusters themselves are associated with larger, non-gravitationally bound, groups called superclusters. Groups of galaxies are the smallest aggregates of galaxies, they contain no more than 50 galaxies in a diameter of 1 to 2 megaparsecs. Their mass is 1013 solar masses; the spread of velocities for the individual galaxies is about 150 km/s. However, this definition should be used as a guide only, as larger and more massive galaxy systems are sometimes classified as galaxy groups.
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 mass range between those of the large elliptical galaxies and clusters of galaxies. Our own Galaxy, the Milky Way, is contained in the Local Group of more than 40 galaxies. In July 2017 S. Paul, R. S. John et al. define clear distinguishing parameters for classifying ‘galaxy groups’ and ‘clusters’ on the basis of scaling laws that they followed. According to this paper, those large scale structures in the universe with mass less than 8 × 1013 solar mass is classified as Galaxy group. Clusters are larger than groups; when observed visually, clusters appear to be collections of galaxies held together by mutual gravitational attraction. However, their velocities are too large for them to remain gravitationally bound by their mutual attractions, implying the presence of either an additional invisible mass component, or an additional attractive force besides gravity.
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, 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 a factor of two. However, this is still not enough mass to keep the galaxies in the cluster. Since this gas is in approximate hydrostatic equilibrium with the overall cluster gravitational field, the total mass distribution can be determined, it turns out the total mass deduced from this measurement is 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 only 5% of the total mass is in the form of galaxies, maybe 10% in the form of hot X-ray emitting gas and the remainder is dark matter. Brownstein and Moffat use a theory of modified gravity to explain X-ray cluster masses without dark matter. Observations of the Bullet Cluster are the strongest evidence for the existence of dark matter.
Clusters of galaxies have been found in surveys by a number of observational techniques and have been studied in detail using many methods: Optical or infrared: The individual galaxies of clusters can be studied through optical or infrared imaging and spectroscopy. Galaxy clusters are found by optical or infrared telescopes by searching for overdensities, 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; the cluster gas can be studied using both X-ray X-ray spectroscopy. Clusters are quite prominent in X-ray surveys and along with AGN are the brightest X-ray emitting extragalactic objects. Radio: A number of diffuse structures emitting at radio frequencies have been found in clusters. Groups of radio sources have been used as tracers of cluster location. At high redshift imaging around individual radio sources has been used to detect proto-clusters.
Sunyaev-Zel'dovich effect: The hot electrons in the intracluster medium scatter radiation from the cosmic microwave background through inverse Compton scattering. This produces a "shadow" in the observed cosmic microwave background at some radio frequencies. Gravitational lensing: Clusters of galaxies contain enough matter to distort the observed orientations of galaxies behind them; the observed distortions can be used to model the distribution of dark matter in the cluster. Clusters of galaxies are the most recent and most massive objects to have arisen in the hierarchical structure formation of the Universe and the study of clusters tells one about the way galaxies form and evolve. Clusters have two important properties: their masses are large enough to retain any energetic gas ejected from member galaxies and the thermal energy of the gas within the cluster is observable within the X-Ray bandpass; the observed state of gas within a cluster is determined by a combination of shock heating during accretion, radiative cooling, thermal feedback triggered by that cooling.
The density and substructure of the intracluster X-Ray gas therefore represents the entire thermal history of cluster formation. To better understand this thermal history one needs to study the entropy of the gas because entropy is the quantity most directly c
The observable universe is a spherical 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 electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. There are at least 2 trillion galaxies in the observable universe. Assuming the Universe is isotropic, the distance to the edge of the observable universe is the same in every direction; that is, the observable universe has a spherical volume centered on the observer. Every location in the Universe has its own observable universe, which may or may not overlap with the one centered on Earth; the 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 physical limit created by the speed of light itself; because no signals can travel faster than light, any object farther away from us than light could travel in the age of the Universe cannot be detected, as the signals could not have reached us yet.
Sometimes astrophysicists distinguish between the visible universe, which includes only signals emitted since recombination —and the observable universe, which includes signals since the beginning of the cosmological expansion. According to calculations, the current comoving distance—proper distance, which takes into account that the universe has expanded since the light was emitted—to particles from which the cosmic microwave background radiation was emitted, which represent the radius of the visible universe, is about 14.0 billion parsecs, while the comoving distance to the edge of the observable universe is about 14.3 billion parsecs, about 2% larger. The radius of the observable universe is therefore estimated to be about 46.5 billion light-years and its diameter about 28.5 gigaparsecs. The total mass of ordinary matter in the universe can be calculated using the critical density and the diameter of the observable universe to be about 1.5 × 1053 kg. In November 2018, astronomers reported that the extragalactic background light amounted to 4 × 1084 photons.
Since the expansion of the universe is known to accelerate and will become exponential in the future, the light emitted from all distant objects, past some time dependent on their current redshift, will never reach the Earth. In the future all observable objects will freeze in time while emitting progressively redder and fainter light. For instance, objects with the current redshift z from 5 to 10 will remain observable for no more than 4–6 billion years. In addition, light emitted by objects situated beyond a certain comoving distance will never reach Earth; some parts of the universe are too far away for the light emitted since the Big Bang to have had enough time to reach Earth or its scientific space-based instruments, so lie outside the observable universe. In the future, light from distant galaxies will have had more time to travel, so additional regions will become observable. However, due to Hubble's law, regions sufficiently distant from the Earth are expanding away from it faster than the speed of light and furthermore the expansion rate appears to be accelerating due to dark energy.
Assuming dark energy remains constant, so that the expansion rate of the universe continues to accelerate, there is a "future visibility limit" beyond which objects will never enter our observable universe at any time in the infinite future, because light emitted by objects outside that limit would never reach the Earth. This future visibility limit is calculated at a comoving distance of 19 billion parsecs, assuming the universe will keep expanding forever, which implies the number of galaxies that we can theoretically observe in the infinite future is only larger than the number observable by a factor of 2.36. Though in principle more galaxies will become observable in the future, in practice an increasing number of galaxies will become redshifted due to ongoing expansion, so much so that they will seem to disappear from view and become invisible. An additional subtlety is that a galaxy at a given comoving distance is defined to lie within the "observable universe" if we can receive signals emitted by the galaxy at any age in its past history, but because of the universe's expansion, there may be some age at which a signal sent from the same galaxy can never reach the Earth at any point in the infinite future (so, for example, we might never see what the galaxy looked like 10 billion years after the Bi
Gérard de Vaucouleurs
Gérard Henri de Vaucouleurs was a French astronomer. Born in Paris, he had an early interest in amateur astronomy and received his undergraduate degree in 1939 at the Sorbonne in that city. After military service in World War II, he resumed his pursuit of astronomy. Fluent in English, he spent 1949–51 in England, 1951–57 in Australia, the latter at Mount Stromlo Observatory, 1957–58 at Lowell Observatory in Arizona and 1958–60 at Harvard. In, 1960 he was appointed to the University of Texas at Austin, where he spent the rest of his career, he died of a heart attack in his home in Austin at the age of 77. His earliest work had concerned the planet Mars and while at Harvard he used telescope observations from 1909 to 1958 to study the areographic coordinates of features on the surface of Mars, his work focused on the study of galaxies and he co-authored the Third Reference Catalogue of Bright Galaxies with his wife Antoinette, a fellow UT Austin astronomer and lifelong collaborator. His specialty included reanalyzing Hubble and Sandage's galaxy atlas and recomputing the distance measurements utilizing a method of averaging many different kinds of metrics such as luminosity, the diameters of ring galaxies, brightest star clusters, etc. in a method he called "spreading the risks."
During the 1950s he promoted the idea. The de Vaucouleurs modified Hubble sequence is a used variant of the standard Hubble sequence. De Vaucouleurs was awarded the Henry Norris Russell Lectureship by the American Astronomical Society in 1988, he was awarded the Prix Jules Janssen of the Société astronomique de France in the same year. He and his wife and longtime collaborator, Antoinette de Vaucouleurs, together produced 400 research and technical papers, 20 books and 100 articles for laymen. De Vaucouleurs' law Edwin Hubble Galaxy color–magnitude diagram William Wilson Morgan Julien Peridier Lahav O. "Galaxies, Human Eyes, Artificial Neural Networks", Science, 267: 859–62, arXiv:astro-ph/9412027, Bibcode:1995Sci...267..859L, doi:10.1126/science.267.5199.859, PMID 17813914 de Vaucouleurs, G, "Tests of the long and short extragalactic distance scales", PNAS, 90: 4811–4813, Bibcode:1993PNAS...90.4811V, doi:10.1073/pnas.90.11.4811, PMC 46605, PMID 11607392 Masursky H. "Mariner 9 Television Reconnaissance of Mars and Its Satellites: Preliminary Results", Science, 175: 294–305, Bibcode:1972Sci...175..294M, doi:10.1126/science.175.4019.294, PMID 17814535 de Vaucouleurs, G.
A supercluster is a large group of smaller galaxy clusters or galaxy groups. The Milky Way is part of the Local Group galaxy group, which in turn is part of the Laniakea Supercluster; this supercluster spans over 500 million light-years, while the Local Group spans over 10 million light-years. The large size and low density of superclusters means they, unlike clusters, expand with the Hubble expansion; the number of superclusters in the observable universe is estimated to be 10 million. The existence of superclusters indicates that the galaxies in the Universe are not uniformly distributed; those groups and clusters and additional isolated galaxies in turn form larger structures called superclusters. Their existence was first postulated by George Abell in his 1958 Abell catalogue of galaxy clusters, he called them clusters of clusters. Superclusters form massive structures of galaxies, called "filaments", "supercluster complexes", "walls" or "sheets", that may span between several hundred million light-years to 10 billion light-years, covering more than 5% of the observable universe.
These are the largest known structures to date. Observations of superclusters can give information about the initial condition of the universe, when these superclusters were created; the directions of the rotational axes of galaxies within superclusters may give insight and information into the early formation process of galaxies in the history of the Universe. Interspersed among superclusters are large voids of space. Superclusters are subdivided into groups of clusters called galaxy groups and clusters. Freedman, Roger. "Galaxies". Universe. New York: W. H. Freedman. ISBN 978-1-319-04238-7. Media related to Superclusters of galaxies at Wikimedia Commons Overview of local superclusters The Nearest Superclusters Universe family tree: Supercluster Superclusters - Large Scale Structures
Harlow Shapley was an American scientist, head of the Harvard College Observatory, political activist during the latter New Deal and Fair Deal. Shapley used RR Lyrae stars to estimate the size of the Milky Way Galaxy and the Sun's position within it by using parallax. In 1953 he proposed his "liquid water belt" theory, now known as the concept of a habitable zone. Shapley was born on a farm in Nashville, Missouri, to Willis and Sarah Shapley, dropped out of school with only the equivalent of a fifth-grade education. After studying at home and covering crime stories as a newspaper reporter, Shapley returned to complete a six-year high school program in only two years, graduating as class valedictorian. In 1907, Shapley went to study journalism at the University of Missouri; when he learned that the opening of the School of Journalism had been postponed for a year, he decided to study the first subject he came across in the course directory. Rejecting Archaeology, which Shapley claimed he could not pronounce, he chose the next subject, Astronomy.
After graduation, Shapley received a fellowship to Princeton University for graduate work, where he studied under Henry Norris Russell and used the period-luminosity relation for Cepheid variable stars to determine distances to globular clusters. He was instrumental in moving astronomy away from the idea that Cepheids were spectroscopic binaries, toward the concept that they were pulsators, he realized that the Milky Way Galaxy was far larger than believed, that the Sun's place in the galaxy was in a nondescript location. This discovery supports the Copernican principle, according to which the Earth is not at the center of our Solar System, our galaxy, or our Universe. Shapley participated in the "Great Debate" with Heber D. Curtis on the nature of nebulae and galaxies and the size of the Universe; the debate took place on April 26, 1920, in the hall of the United States National Academy of Sciences in Washington D. C. Shapley took the side that spiral nebulae are inside our Milky Way, while Curtis took the side that the spiral nebulae are'island universes' far outside our own Milky Way and comparable in size and nature to our own Milky Way.
This issue and debate are the start of extragalactic astronomy, while the detailed arguments and data with ambiguities, appeared together in 1921. Characteristic issues were whether Adriaan van Maanen had measured rotation in a spiral nebula, the nature and luminosity of the exploding novae and supernovae seen in spiral galaxies, the size of our own Milky Way. However, Shapley's actual talk and argument given during the Great Debate were different from the published paper. Historian Michael Hoskin says "His decision was to treat the National Academy of Sciences to an address so elementary that much of it was uncontroversial.", with Shapley's motivation being only to impress a delegation from Harvard who were interviewing him for a possible offer as the next Director of Harvard College Observatory. With the default by Shapley, Curtis won the debate; the astronomical issues were soon resolved in favor of Curtis' position when Edwin Hubble discovered Cepheid variable stars in the Andromeda Galaxy.
At the time of the debate, Shapley was working at the Mount Wilson Observatory, where he had been hired by George Ellery Hale. After the debate, however, he was hired to replace the deceased Edward Charles Pickering as director of the Harvard College Observatory, he is known to have incorrectly opposed Edwin Hubble's observations that there are additional galaxies in the universe other than the Milky Way. Shapley fiercely regarded his work as junk science. However, after he received a letter from Hubble showing Hubble's observed light curve of V1, he withdrew his criticism, he told a colleague, "Here is the letter that destroyed my universe." He encouraged Hubble to write a paper for a joint meeting of the American Astronomical Society and American Association for the Advancement of Science. Hubble's findings went on to reshape fundamentally the scientific view of the universe, he served as director of the HCO from 1921–52. During this time, he hired Cecilia Payne, who, in 1925, became the first person to earn a doctorate at Radcliffe College in the field of astronomy, for work done at Harvard College Observatory.
From 1941 he was on the original standing committee of the Foundation for the Study of Cycles. He served on the board of trustees of Science Service, now known as Society for Science & the Public, from 1935-71. In the 1940s, Shapley helped found government funded scientific associations, including the National Science Foundation, he is responsible for the addition of the "S" in UNESCO. On November 14, 1946, Shapley appeared under subpoena by the House Un-American Activities Committee in his role as member of the Independent Committee of the Arts and Professions, "major political arm of the Russophile left", for opposing U. S. Representative Joseph William Martin Jr. during mid-term elections that year. In 1947, he became President of the American Association for the Advancement of Science. In his inaugural address he referred to the danger of the "genius maniac" and proposed the elimination of "all primates that show any evidence of signs of genius or talent". Other global threats he listed were: drugs.
In 1950, Shapley was instrumental in organizing a campaign in academia against the controversial US bestseller book Worlds in