It proves that some dead galaxies transform from a disk into a massive elliptical galaxies.
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These ancient galaxies are thought to be the ancestors of today's elliptical galaxies, according to a press release.
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These random or non-planar orbits are found in the round bulges of spiral galaxies and in elliptical galaxies.
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To make matters more strange, it also has no central black hole, as is typically found in elliptical galaxies.
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Before infirmity sets in, some freshly formed elliptical galaxies experience a final flush of youth, as is the case with NGC 3597.
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Astronomers suspect that some irregular dwarf galaxies were once spiral or elliptical galaxies, but were later deformed by the gravitational pull of nearby objects.
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For example, it has long been assumed that huge crashes destroy the disks of spiral galaxies, turning these gorgeous objects into rather drab elliptical galaxies.
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Astronomers study NGC 3597 to learn more about how elliptical galaxies form — many ellipticals began their lives far earlier in the history of the universe.
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Elliptical galaxies will also exhibit a range of projected elongations (from fairly narrow ellipses to circles), but will be rounder on average than spiral galaxies.
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Video: NASA Goddard/YouTube Most of the gamma rays in the above video were generated by blazars, which are compact elliptical galaxies anchored by supermassive black holes.
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KornmesserRachel BezansonObservational Astronomer, University of PittsburghGalaxies in the nearby Universe come in two basic types: flattened disk-like spirals, like our Milky Way, and rounder, more spherical, elliptical galaxies.
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If you rank-order galaxies by the ratio of bulge to disk size, eventually you start to find galaxies with no obvious disk at all—which we call elliptical galaxies.
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If you look closely at the photo, you should be able to see spiral galaxies that look like our own along with yellow-tinged elliptical galaxies that don't look as familiar.
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For years, astronomers have presumed that this object, known as Sagittarius A*, was a supermassive black hole, which are known to be at the center of most spiral and elliptical galaxies.
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The population of clusters is dependent on the galaxy&aposs size; huge elliptical galaxies can boast tens of thousands of globular clusters, while our own Milky Way holds around 200 such clusters.
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These peculiar galaxies are like a natural experiment played out on a cosmic scale and by cataloguing them, astronomers can better understand the physical processes that warp spiral and elliptical galaxies into new shapes.
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There are elliptical galaxies in the universe today, so it's possible that ones like ZF-COSMOS-20115 are now the chocolatey centers of other far more massive galaxies, but we don't know for sure.
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At the center of our galaxy lies colossal black hole with the mass of four million Suns, called Sagittarius A*. Scientists think spiral and elliptical galaxies like the Milky Way contain these beefed-up black holes at their cores, but what has been more difficult to quantify is the population of smaller black holes in the immediate vicinity of these central giants.
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I tested it on the abstract for an epidemiological study of a skin condition, for example, and got a very mixed bag of results — including research papers on elliptical galaxies, the cultural evolution of co-operation, and a paper on the effects of low flush water closets in buildings and their impact on draining systems… Now it might be there's a brilliant robot medical dermatological hypothesis being forged by a budding machine intellect that connects the dots of poorly designed toilets with compassionate cultural leanings and a little galactic wonkiness but I doubt it.
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Dwarf elliptical galaxies, or dEs, are elliptical galaxies that are smaller than ordinary elliptical galaxies. They are quite common in galaxy groups and clusters, and are usually companions to other galaxies.
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Dwarf elliptical galaxies have blue absolute magnitudes within the range −18 mag < M < −14 mag, fainter than ordinary elliptical galaxies. The surface brightness profiles of ordinary elliptical galaxies used to be approximated with de Vaucouleur's model, while dEs were approximated with an exponentially declining surface brightness profile. However, both types can be well fit by the same more general function, known as Sersic's model, and there is a continuity of Sersic index - which quantifies the shape of the surface brightness profile - as a function of galaxy luminosity,A. Graham and R. Guzman (2003), HST Photometry of Dwarf Elliptical Galaxies in Coma, and an Explanation for the Alleged Structural Dichotomy between Dwarf and Bright Elliptical Galaxies revealing that dwarf and ordinary elliptical galaxies belong to a single sequence.
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The Fish law (or Fish's law) in astronomy is the analogue for the Freeman law with disk galaxies replaced by elliptical galaxies. It was described in 1964 by Robert A. Fish based on photometric results for 29 elliptical galaxies.
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The mass of the black hole is also correlated to a property called sigma which is the dispersion of the velocities of stars in their orbits. This relationship, known as the M-sigma relation, was discovered in 2000. Elliptical galaxies mostly lack disks, although some bulges of disk galaxies resemble elliptical galaxies. Elliptical galaxies are more likely found in crowded regions of the universe (such as galaxy clusters).
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The motion of stars in elliptical galaxies is predominantly radial, unlike the disks of spiral galaxies, which are dominated by rotation. Furthermore, there is very little interstellar matter (neither gas nor dust), which results in low rates of star formation, few open star clusters, and few young stars; rather elliptical galaxies are dominated by old stellar populations, giving them red colors. Large elliptical galaxies typically have an extensive system of globular clusters. The dynamical properties of elliptical galaxies and the bulges of disk galaxies are similar, suggesting that they may be formed by the same physical processes, although this remains controversial.
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Elliptical galaxies are preferentially found in galaxy clusters and in compact groups of galaxies. Unlike flat spiral galaxies with organization and structure, elliptical galaxies are more three-dimensional, without much structure, and their stars are in somewhat random orbits around the center.
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Many elliptical galaxies are believed to form due to the interaction of galaxies, resulting in a collision and merger. They can grow to enormous sizes (compared to spiral galaxies, for example), and giant elliptical galaxies are often found near the core of large galaxy clusters.
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Elliptical galaxies range in size from tens of millions to over one hundred trillion stars. Originally, Edwin Hubble hypothesized that elliptical galaxies evolved into spiral galaxies, which was later discovered to be false,John, D. (2006). Astronomy: The definitive guide to the universe. Bath, UK: Parragon Publishing.
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In contrast, dwarf elliptical galaxies, dwarf irregular galaxies, and the dwarf versions of Magellanic type galaxies (which may be considered transitory between spiral and irregular in terms of morphology) are very common. It is suggested that dwarf spiral galaxies can transform into dwarf elliptical galaxies, especially in dense cluster environments.
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He also concluded in a later experiment that elliptical galaxies are generally older than spiral galaxies, among other discoveries.
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The of elliptical galaxies paints them as galaxies where star formation finished after an initial burst at high-redshift, leaving them to shine with only their aging stars. Elliptical galaxies typically appear yellow-red, which is in contrast to the distinct blue tinge of most spiral galaxies. In spirals, this blue color emanates largely from the young, hot stars in their spiral arms. Very little star formation is thought to occur in elliptical galaxies, because of their lack of gas compared to spiral or irregular galaxies.
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ULXs are found in all types of galaxies, including elliptical galaxies but are more ubiquitous in star-forming galaxies and in gravitationally interacting galaxies. Tens of percents of ULXs are in fact background quasars; the probability for a ULX to be a background source is larger in elliptical galaxies than in spiral galaxies.
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Minkowski, R. (1962), Internal Dispersion of Velocities in Other Galaxies This was important because the value of \gamma depends on the range of galaxy luminosities that is fitted, with a value of 2 for low-luminosity elliptical galaxies discovered by a team led by Roger Davies,Davies, R. L.; Efstathiou, G.; Fall, S. M.; Illingworth, G.; Schechter, P. L. (1983), The kinematic properties of faint elliptical galaxies and a value of 5 reported by Paul L. Schechter for luminous elliptical galaxies.Paul L. Schechter (1980), Mass-to-light ratios for elliptical galaxies The Faber–Jackson relation is understood as a projection of the Fundamental Plane of elliptical galaxies. One of its main uses is as a tool for determining distances to external galaxies.
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Subdwarf B stars, being more luminous than white dwarfs, are a significant component in the hot star population of old stellar systems, such as globular clusters, spiral galaxy bulges and elliptical galaxies. They are prominent on ultraviolet images. The hot subdwarfs are proposed to be the cause of the UV upturn in the light output of elliptical galaxies.
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Martha Liller (1966), The Distribution of Intensity in Elliptical Galaxies of the Virgo Cluster. II Gorbachev, V.I. (1970), The Central Part of the Coma Cluster of Galaxies Observations of the kinematics of early-type galaxies further confirmed this.Graham, Alister W.; Colless, Matthew M.; Busarello, Giovanni; Zaggia, Simone; Longo, Giuseppe (1998), Extended stellar kinematics of elliptical galaxies in the Fornax clusterEmsellem, Eric, et al.
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Elliptical galaxies (such as IC 1101) are among some of the largest known thus far. Their stars are on orbits that are randomly oriented within the galaxy (i.e. they are not rotating like disk galaxies). A distinguishing feature of elliptical galaxies is that the velocity of the stars does not necessarily contribute to flattening of the galaxy, such as in spiral galaxies.
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The studies found that elliptical galaxies were the oldest and formed from the violent merger of other galaxies about two to three billion years after the Big Bang. Star formation in elliptical galaxies ceased about that time. On the other hand, new stars are still forming in the spiral arms of spiral galaxies. Lenticular galaxies (SO) are intermediate between the first two.
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Distribution of stellar populations within a galaxy varies between the different types of galaxies.Habitable Zones in the Universe, G. Gonzalez, (Submitted on March 14, 2005 (v1), last revised March 21, 2005 (this version, v2)) Stars in elliptical galaxies are much older than stars in spiral galaxies. Most elliptical galaxies contain mainly low-mass stars, with minimal star-formation activity.John, D, (2006), Astronomy, , p.
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NGC 4782 and NGC 4783 are a pair of merging elliptical galaxies in the northeastern part of the constellation, around 200 million light-years distant.
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Elliptical galaxies have central supermassive black holes, and the masses of these black holes correlate with the galaxy's mass. Elliptical galaxies have two main stages of evolution. The first is due to the supermassive black hole growing by accreting cooling gas. The second stage is marked by the black hole stabilizing by suppressing gas cooling, thus leaving the elliptical galaxy in a stable state.
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Lenticular galaxies like these are thought to be intermediate between spiral galaxies and elliptical galaxies, and like elliptical galaxies, they have very little gas for star formation. IC 335 may have once been a spiral galaxy that ran out of interstellar medium, or it may have collided with a galaxy in the past and thus used up all of its gas (See Interacting galaxy).
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Elliptical galaxies are thought to form from collisions with spiral galaxies; NGC 3610 is a relatively young elliptical galaxy which has still not lost its disk yet.
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NGC 1460 is also an early-type galaxy. Despite their name, early-type galaxies are much older than spiral galaxies, and mostly comprise old, red-colored stars. Very little star formation occurs in these galaxies; the lack of star formation in elliptical galaxies appears to start at the center and then slowly propagates outward. This galaxy is early-type lenticular, but lenticular galaxies have as same process as elliptical galaxies.
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224-225 The distribution of the different types of galaxies in the universe depends on their location within galaxy clusters, with elliptical galaxies found mostly close to their centers.
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B-type subdwarfs, being more luminous than white dwarfs, are a significant component in the hot star population of old stellar systems, such as globular clusters and elliptical galaxies.
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One of the largest galaxy mergers ever observed consisted of four elliptical galaxies in the cluster CL0958+4702. It may form one of the largest galaxies in the Universe.
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NGC 5846 harbors a large number of globular clusters; over 1,200 have been detected in images by Hubble Space Telescope. The specific frequency is similar to other elliptical galaxies in groups. As has been observed in other large elliptical galaxies, the metallicity has bimodial distribution, with metallicities roughly of [Fe/H]=-1.2 and -0.2. Their typical effective radii are in the range of 3 - 5 pc, with the largest clusters located in the central regions.
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Despite their name, early-type galaxies are much older than spiral galaxies, and mostly comprise old, red-colored stars. Very little star formation occurs in these galaxies; the lack of star formation in elliptical galaxies appears to start at the center and then slowly propagates outward. This is an early-type lenticular galaxy, with similar nature to early-type elliptical galaxies. NGC 1387 is rich with globular clusters, with an estimated number of clusters of 406 ± 81.
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Astronomers now see elliptical galaxies as some of the most evolved systems in the universe. It is widely accepted that the main driving force for the evolution of elliptical galaxies is mergers of smaller galaxies. Many galaxies in the universe are gravitationally bound to other galaxies, which means that they will never escape their mutual pull. If the galaxies are of similar size, the resultant galaxy will appear similar to neither of the progenitors, but will instead be elliptical.
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Massive elliptical galaxies have high Sérsic indices and a high degree of central concentration. This galaxy, M87, has a Sérsic index n~ 4. G. Savorgnan et al. (2013),The supermassive black hole mass-Sérsic index relations for bulges and elliptical galaxies Discs of spiral galaxies, such as the Triangulum Galaxy, have low Sérsic indices and a low degree of central concentration. Most galaxies are fit by Sérsic profiles with indices in the range 1/2 < n < 10\.
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These radio sources are almost universally found hosted by elliptical galaxies, though there is one well- documented exception, namely NGC 4151. Some Seyfert galaxies show weak, small radio jets, but they are not radio-luminous enough to be classified as radio- loud. Such information as there is about the host galaxies of radio-loud quasars and blazars suggests that they are also hosted by elliptical galaxies. There are several possible reasons for this very strong preference for ellipticals.
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The fundamental plane is a set of bivariate correlations connecting some of the properties of normal elliptical galaxies. Some correlations have been empirically shown. The fundamental plane is usually expressed as a relationship between the effective radius, average surface brightness and central velocity dispersion of normal elliptical galaxies. Any one of the three parameters may be estimated from the other two, as together they describe a plane that falls within their more general three-dimensional space.
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The luminosity profiles of both elliptical galaxies and bulges are well fit by Sersic's law, and a range of scaling relations between the elliptical galaxies' structural parameters unify the population.Graham, A.W. (2013), Elliptical and Disk Galaxy Structure and Modern Scaling Laws Every massive elliptical galaxy contains a supermassive black hole at its center. Observations of 46 elliptical galaxies, 20 classical bulges, and 22 pseudobulges show that each contain a black hole at the center. The mass of the black hole is tightly correlated with the mass of the galaxy,Graham, A.W. (2016), Galaxy Bulges and Their Massive Black Holes: A Review evidenced through correlations such as the M–sigma relation which relates the velocity dispersion of the surrounding stars to the mass of the black hole at the center.
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Stars in bound systems must obey the virial theorem. The theorem, together with the measured velocity distribution, can be used to measure the mass distribution in a bound system, such as elliptical galaxies or globular clusters. With some exceptions, velocity dispersion estimates of elliptical galaxies do not match the predicted velocity dispersion from the observed mass distribution, even assuming complicated distributions of stellar orbits. As with galaxy rotation curves, the obvious way to resolve the discrepancy is to postulate the existence of non-luminous matter.
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The dwarf elliptical galaxies within Coma have their own internal velocity dispersion for their stars, which is a σ ≲ 80 km/s, typically. Normal elliptical galaxies, by comparison, have an average σ ≈ 200 km/s. For spiral galaxies, the increase in velocity dispersion in population I stars is a gradual process which likely results from the random momentum exchanges, known as dynamical friction, between individual stars and large interstellar media (gas and dust clouds) with masses greater than . Face-on spiral galaxies have a central σ ≲ 90 km/s; slightly more if viewed edge-on.
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IINieto, J.-L. et al. (1988), More isotropic oblate rotators in elliptical galaxiesGraham, A.W. et al. (2016), Disky Elliptical Galaxies and the Allegedly Over-massive Black Hole in the Compact “ES“ Galaxy NGC 1271 (see their Fig.7).
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The diagram has three main features: the red sequence, the green valley, and the blue cloud. The red sequence includes most red galaxies, which are generally elliptical galaxies. The blue cloud includes most blue galaxies, which are generally spirals.
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Both are located in central part of the Fornax Cluster. NGC 1379 has a Hubble classification of E0, which indicates it is no flattened galaxy. It is also an early-type galaxy, like most other elliptical galaxies in the Fornax Cluster.
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Lauer studied Astronomy at the California Institute of Technology and graduated with a BS degree in 1979. He received his PhD degree in Astronomy from the University of California, Santa Cruz in 1983 for High resolution surface photometry of elliptical galaxies.
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If we took Milky Way as the standard of mass, it may be close to 8 trillion solar masses. However, as NGC 4889 is a spheroid, and not a flat spiral, it has a three-dimensional profile, so it may be as high as 15 trillion solar masses. However, as for elliptical galaxies, only a small fraction of the mass of NGC 4889 is in the form of stars that radiate energy. Assuming a mass to light ratio of 6.5 as with other elliptical galaxies, NGC 4889 may be a thousand times more massive than the Milky Way.
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Possibly, a third, SN 1980I is part of M84 or, alternatively, one of its neighboring galaxies, NGC 4387 and M86. This high rate of supernova events is rare for elliptical galaxies, which may indicate there is a population of stars of intermediate age in M84.
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The galaxy may be a counterpart to the rectangular-shaped galaxy LEDA 74886, in that they both appear to contain an intermediate-scale disk. In the case of LEDA 74886, that disk is orientated edge-on to our line-of-sight. The "early-type galaxy" class is commonly known to contain elliptical galaxies (E) with no substantial stellar disk (perhaps just a small nuclear disk) and lenticular galaxies (S0) with their large-scale disks that dominate the light at large radii. Bridging these two types of galaxies are the ES galaxiesLiller, M.H. (1966), The Distribution of Intensity in Elliptical Galaxies of the Virgo Cluster.
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Despite their name, early-type galaxies are much older than spiral galaxies, and mostly comprise old, red-colored stars. Very little star formation occurs in these galaxies; the lack of star formation in elliptical galaxies appears to start at the center and then slowly propagates outward.
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The law is named for the astronomers Edwin Hubble and John Henry Reynolds. It was first formulated by Reynolds in 1913 from his observations of galaxies (then still known as nebulae). It was later re-derived by Hubble in 1930 specifically in observations of elliptical galaxies.
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NGC 3610 is an elliptical galaxy in the constellation Ursa Major. It was discovered on 8 April 1793 by William Herschel. NGC 3610 was imaged by the Hubble Space Telescope in 2015. The image shows a prominent disk, a characteristic of spiral galaxies but not elliptical galaxies.
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Elliptical galaxy IC 2006. Elliptical galaxies are characterized by several properties that make them distinct from other classes of galaxy. They are spherical or ovoid masses of stars, starved of star-making gases. The smallest known elliptical galaxy is about one-tenth the size of the Milky Way.
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The host galaxies are almost exclusively large elliptical galaxies. Radio-loud active galaxies can be detected at large distances, making them valuable tools for observational cosmology. Recently, much work has been done on the effects of these objects on the intergalactic medium, particularly in galaxy groups and clusters.
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The NGC 4065 Group is a group of galaxies located about in the constellation Coma Berenices. The group's brightest member is NGC 4065 and located in the Coma Supercluster. The group is dominated by mostly elliptical galaxies with only 15 to 31 percent of the members being spiral galaxies.
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Its ring is symmetric, implying that the dust has settled in this galaxy, after the galaxy merger with a relatively gas rich galaxy that led to its creation. The core of NGC 4494 is kinematically decoupled, as with many elliptical galaxies, probably a result of a galaxy merger.
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Beth A. Brown (July 15, 1969 – October 5, 2008) was a NASA astrophysicist with a research focus on X-ray observations of elliptical galaxies and black holes. She earned a Ph.D. in Astronomy from the University of Michigan in 1998, becoming the first African-American woman to do so.
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Arp 166 is a pair of interacting elliptical galaxies approximately 225 million light-years away from Earth in the constellation of Triangulum. The two galaxies, NGC 750 and NGC 751, are listed together as Arp 166 in the Atlas of Peculiar Galaxies (in the category Galaxies with diffuse filaments).
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NGC 4696 is an elliptical galaxy. It lies around away in the constellation Centaurus. It is the brightest galaxy in the Centaurus Cluster, a large, rich cluster of galaxies in the constellation of the same name. The galaxy is surrounded by many dwarf elliptical galaxies also located within the cluster.
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The first consists of elliptical galaxies that seem to be roughly as old as the universe. The second subpopulation contains red-sequence lenticular (lens shaped) galaxies whose ages are directly tied to their mass. The third and final subpopulation is of galaxies where star formation is still taking place, and are morphologically distributed.
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The brightest elliptical galaxies often have low-density cores that are not well described by Sérsic's law. The core-Sérsic family of models was introduced A. Graham et al. (2003), A New Empirical Model for the Structural Analysis of Early-Type Galaxies, and A Critical Review of the Nuker ModelI. Trujillo et al.
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Strings of red H II regions delineate the arms of the Whirlpool Galaxy. H II regions are found only in spiral galaxies like the Milky Way and irregular galaxies. They are not seen in elliptical galaxies. In irregular galaxies, they may be dispersed throughout the galaxy, but in spirals they are most abundant within the spiral arms.
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The giant elliptical galaxy ESO 325-G004. On the left (in the sense that the sequence is usually drawn) lie the ellipticals. Elliptical galaxies have relatively smooth, featureless light distributions and appear as ellipses in photographic images. They are denoted by the letter E, followed by an integer n representing their degree of ellipticity in the sky.
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The cluster's largest galaxies are elliptical galaxies NGC 3309 and NGC 3311 and the spiral galaxy NGC 3312 all having a diameter of about 150,000 light-years.The Hydra Supercluster An Atlas of the Universe.com In spite of a nearly circular appearance on the sky, there is evidence in the galaxy velocities for a clumpy, three-dimensional distribution.
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Spiral DRAGNs are a type of galaxy; spiral galaxies which contain DRAGNs (Double Radio-source Associated with Galactic Nucleus), and are therefore also radio galaxies. Most DRAGNs are associated with elliptical galaxies, as are most double-lobed radio-galaxies. Spiral DRAGNs are inconsistent with currently known galaxy formation processes. As of 2015, there are 4 known spiral DRAGNs.
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A large spiral galaxy may contain thousands of H II regions. The reason H II regions rarely appear in elliptical galaxies is that ellipticals are believed to form through galaxy mergers. In galaxy clusters, such mergers are frequent. When galaxies collide, individual stars almost never collide, but the GMCs and H II regions in the colliding galaxies are severely agitated.
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NGC 3597 is the product of a collision between two galaxies. It is evolving into a giant elliptical galaxy. It is widely accepted that the merging of smaller galaxies due to gravitational attraction plays a major role in shaping the growth and evolution of elliptical galaxies. Such major galactic mergers are thought to have been more common at early times.
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Although it appears that globular clusters contain some of the first stars to be produced in the galaxy, their origins and their role in galactic evolution are still unclear. It does appear clear that globular clusters are significantly different from dwarf elliptical galaxies and were formed as part of the star formation of the parent galaxy, rather than as a separate galaxy.
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The Stebbins–Whitford effect refers to the excess reddening of the spectra of elliptical galaxies as shown by measurements published by Joel Stebbins and Albert Whitford In 1948. The spectra were shifted much more to the red than the Hubble redshift could account for. Furthermore, this excess reddening increased with the distance of the galaxies. Cosmology and Controversy by Helge Kragh.
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Chandra image of the core of NGC 4636 with superimposed contours of Hα+[N ii] emission. White crosses mark the detected CO cloud positions. NGC 4636 is one of the most luminous nearby elliptical galaxies when observed in X-rays, with estimated X-ray flux of erg/s. A hot gas corona around the galaxy was first detected by the Einstein Observatory.
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M32's unusual characteristics of dense compactness and burst of star formation 2 billion years ago would be explained by this theory as a remnant of an earlier large galaxy, given its unlikeness to other similarly sized elliptical galaxies. It was described in 2018 by scientists at the University of Michigan. It is thought to have been 2.5×1010 M☉ in size.
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Some irregular galaxies were once spiral or elliptical galaxies but were deformed by an uneven external gravitational force. Irregular galaxies may contain abundant amounts of gas and dust.Faulkes Telescope Educational Guide - Galaxies - Irregulars This is not necessarily true for dwarf irregulars.Walter, F. et al. Astophys J 661, 102 - 114, 2007 Irregular galaxies are commonly small, about one tenth the mass of the Milky Way galaxy.
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In his later years he made significant contributions toward understanding the dynamics of elliptical galaxies. Schwarzschild was renowned as a teacher and held major leadership positions in several scientific societies. In the 1980s, Schwarzschild applied his numerical skills to building models for triaxial galaxies. Dr. Schwarzschild was the Eugene Higgins Professor Emeritus of Astronomy at Princeton University, where he spent most of his professional life.
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Most dense galaxy clusters are composed mostly of elliptical galaxies. The Leo Cluster, however, mostly contains spiral galaxies, suggesting that it is much younger than other comparable clusters, such as the Coma Cluster. It is also home to one of the universe's largest known black holes, which lies in the center of NGC 3842. The black hole is 9.7 billion times more massive than our sun.
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The D–σ relation, used in elliptical galaxies, relates the angular diameter (D) of the galaxy to its velocity dispersion. It is important to describe exactly what D represents, in order to understand this method. It is, more precisely, the galaxy's angular diameter out to the surface brightness level of 20.75 B-mag arcsec−2. This surface brightness is independent of the galaxy's actual distance from us.
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Its ten brightest spiral galaxies have apparent magnitudes of 12–14 that are observable with amateur telescopes larger than 20 cm. The central region is dominated by two supergiant elliptical galaxies: NGC 4874 and NGC 4889. The cluster is within a few degrees of the north galactic pole on the sky. Most of the galaxies that inhabit the central portion of the Coma Cluster are ellipticals.
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Planetary nebula luminosity function (PNLF) is a secondary distance indicator used in astronomy. It makes use of the [O III] λ5007 forbidden line found in all planetary nebula (PNe) which are members of the old stellar populations (Population II). It can be used to determine distances to both spiral and elliptical galaxies despite their completely different stellar populations and is part of the Extragalactic Distance Scale.
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The gamma ray bursts from the galaxy extend out to several million light years of the cluster. As with other similar elliptical galaxies, only a fraction of the mass of NGC 4889 is in the form of stars. They have a flattened, unequal distribution that bulges within its edge. Between the stars is a dense interstellar medium full of heavy elements emitted by evolved stars.
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She studied elliptical galaxies using HI emissions. She returned to the University of North Carolina at Greensboro as a research associate, where she worked until 1984. In 1984 Williams was appointed as a postdoctoral fellow at the University of North Carolina at Chapel Hill. She spent a year as a NASA-American Society for Engineering Education summer faculty member at the Goddard Space Flight Center.
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Elliptical and lenticular galaxies are commonly referred to together as “early-type” galaxies, while spirals and irregular galaxies are referred to as “late types”. This nomenclature is the source of the common, but erroneous, belief that the Hubble sequence was intended to reflect a supposed evolutionary sequence, from elliptical galaxies through lenticulars to either barred or regular spirals. In fact, Hubble was clear from the beginning that no such interpretation was implied: > The nomenclature, it is emphasized, refers to position in the sequence, and > temporal connotations are made at one's peril. The entire classification is > purely empirical and without prejudice to theories of evolution... The evolutionary picture appears to be lent weight by the fact that the disks of spiral galaxies are observed to be home to many young stars and regions of active star formation, while elliptical galaxies are composed of predominantly old stellar populations.
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The central galaxy in this image is a gigantic elliptical galaxy designated 4C 73.08. The brilliant central object is a supergiant elliptical galaxy, the dominant member of a galaxy cluster with the name MACSJ1423.8+2404. Note the gravitational lensing. Elliptical galaxies vary greatly in both size and mass with diameters ranging from 3000 lightyears to more than 700,000 lightyears, and masses from 105 to nearly 1013 solar masses.
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NGC 3312 appears to be highly distorted with sharp dust lanes. There are sharp filamentary extensions to the north and an internal ringlike structure in the galaxy. The interstellar matter in the galaxy also appears highly disturbed. These features caused astronomer De Vaucouleurs to suggest that NGC 3312 was distorted by the giant elliptical galaxies NGC 3309 and NGC 3311 which are the dominant ellipticals in the Hydra Cluster.
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NGC 4555 is a solitary elliptical galaxy about 40,000 parsecs (125,000 light- years) across, and about 310 million light years distant. Observations by the Chandra X-ray Observatory have shown it to be surrounded by a halo of hot gas about 120,000 parsecs across. The hot gas has a temperature of around 10,000,000 kelvins. The galaxy is one of the few elliptical galaxies proven to have significant amounts of dark matter.
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The Davis–Greenstein effect causes elongated dust grains to align themselves with a galaxy's magnetic field, resulting in weak optical polarization. This has been used to show ordered magnetic fields exist in several nearby galaxies. Magneto-hydrodynamic processes in active elliptical galaxies produce their characteristic jets and radio lobes. Non-thermal radio sources have been detected even among the most distant, high-z sources, indicating the presence of magnetic fields.
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There are nearly 130 globular cluster candidates in the galaxy, with the total number of globular clusters estimated to be nearly 550. This number is quite low, but it is typical for field elliptical galaxies. Based on luminosity turnover of the globular clusters, it is suspected that there is a subpopulation of younger clusters. The outer isophotes of the galaxy are asymmetrical, maybe due to a tidal disruption.
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This galaxy has a morphological classification of pec dE5, indicating a dwarf elliptical galaxy with a flattening of 50%. M110 is designated peculiar because there are patches of dust and young blue stars located near the center. This is unusual for dwarf elliptical galaxies in general, and the reason for this peculiarity is unclear. Unlike M32, M110 does not show evidence for a supermassive black hole at its center.
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An early stage merger in this case can also be identified as a LIRG. After that, it becomes a late stage merger, which is a ULIRG. It then becomes a quasar and in the final stage of the evolution it becomes an elliptical galaxy. This can be evidenced by the fact that stars are much older in elliptical galaxies than those found in the earlier stages of the evolution.
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Elliptical galaxies are spherical or elliptical in appearance. Spiral galaxies range from S0, the lenticular galaxies, to Sb, which have a bar across the nucleus, to Sc galaxies which have strong spiral arms. In total count, ellipticals amount to 13%, S0 to 22%, Sa, b, c galaxies to 61%, irregulars to 3.5% and peculiars to 0.9%. At the center of the most galaxies is a high concentration of older stars.
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M87 is about from Earth and is the second-brightest galaxy within the northern Virgo Cluster, having many satellite galaxies. Unlike a disk-shaped spiral galaxy, M87 has no distinctive dust lanes. Instead, it has an almost featureless, ellipsoidal shape typical of most giant elliptical galaxies, diminishing in luminosity with distance from the center. Forming around one-sixth of its mass, M87's stars have a nearly spherically symmetric distribution.
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Stellar dynamics also provides insight into the structure of galaxy formation and evolution. Dynamical models and observations are used to study the triaxial structure of elliptical galaxies and suggest that prominent spiral galaxies are created from galaxy mergers. Stellar dynamical models are also used to study the evolution of active galactic nuclei and their black holes, as well as to estimate the mass distribution of dark matter in galaxies.
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The galaxy has a high rotational velocity, estimated to be 120 ± 10 km/s, higher than that of other elliptical galaxies of similar luminosity. The HI mass of the galaxy is estimated to be and the mass of HII less than . In the centre of NGC 3640 lies a supermassive black hole whose mass is estimated to be roughly 100 million (107.99 ± 0.39) based on the Sérsic profile.
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Her research considers how cosmic dust grains form in elliptical galaxies. She has used the Akari satellite to survey the sky in the mid-infrared and identify the building blocks of life. Gomez continued to use the data from the Herschel Space Observatory long after it stopped operating in 2013. As Head of Public Engagement in the School of Physics at Cardiff University, Gomez coordinates the outreach activities for schools, teachers and the public.
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The Hubble classification system rates elliptical galaxies on the basis of their ellipticity, ranging from E0, being nearly spherical, up to E7, which is highly elongated. These galaxies have an ellipsoidal profile, giving them an elliptical appearance regardless of the viewing angle. Their appearance shows little structure and they typically have relatively little interstellar matter. Consequently, these galaxies also have a low portion of open clusters and a reduced rate of new star formation.
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Where C is a constant which depends on the distance to the galaxy clusters. This method has the potential to become one of the strongest methods of galactic distance calculators, perhaps exceeding the range of even the Tully–Fisher method. As of today, however, elliptical galaxies aren't bright enough to provide a calibration for this method through the use of techniques such as Cepheids. Instead, calibration is done using more crude methods.
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Moreover, the galaxy, contrary to most elliptical galaxies which lack neutral hydrogen emission, has been found to possess a massive HI disk, probably formed after the accretion of a dwarf satellite galaxy. The total mass of the HI disk is estimated to be . The disk rotates at the same sense as the stars, but is misaligned by 20° to 70°. Molecular clouds, as pointed by CO emission, have also been detected in the galaxy.
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The galaxy has been observed with the InfraRed Spectrograph (IRS) onboard Spitzer Space Telescope, examining the dust features of NGC 4278. Multiphase gas and dust have been observed in the same elongated features. Another uncommon finding for an elliptical galaxy is the detection of emission by polycyclic aromatic hydrocarbons (PAHs) and of strong [Si II] 34.8-μm emission. PAHs in other elliptical galaxies are believed to be destroyed by the hot interstellar medium.
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The stellar halo is a nearly spherical population of field stars and globular clusters. It surrounds most disk galaxies as well as some elliptical galaxies of type cD. A low amount (about one percent) of a galaxy's stellar mass resides in the stellar halo, meaning its luminosity is much lower than other components of the galaxy. The Milky Way's stellar halo contains globular clusters, RR Lyrae stars with low metal content, and subdwarfs.
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She earned her M.S. in astronomy from the University of Michigan and a Ph.D. from there in 1998. She was the first African-American woman to earn a Ph.D. from the University of Michigan's Department of Astronomy. While at the University of Michigan, she developed a one-credit course in "naked eye astronomy" for students with no experience in astronomy. Her research there concerned X-ray observations of elliptical galaxies from the Röntgen Satellite.
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It is a type-cD galaxy, with a bright center and a vast, diffuse envelope surrounding it. It is also an early-type galaxy, the largest one in the Fornax Cluster. Despite their name, early-type galaxies are much older than spiral galaxies, and mostly comprise old, red-colored stars. Very little star formation occurs in these galaxies; the lack of star formation in elliptical galaxies appears to start at the center and then slowly propagates outward.
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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 very large elliptical galaxies and clusters of galaxies. Our own Galaxy, the Milky Way, is contained in the Local Group of more than 54 galaxies.
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The NGC 4065 Group appears to consist of two subgroups known as UZC-CG 156 and UZC-CG 157 which are indistinguishable by velocity. However, White et al. suggests that the group contains three subgroups with subgroups A and C being centered on NGC 4065 and NGC 4095 respectively, and subgroup B which consists of the galaxies NGC 4086 and NGC 4090. At the center of the group lie the elliptical galaxies NGC 4061 and NGC 4065.
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An image of Messier 81, a galaxy with a classical bulge. The spiral structure ends at the onset of the bulge. Bulges that have properties similar to those of elliptical galaxies are often called "classical bulges" due to their similarity to the historic view of bulges.Sandage, Allan, The Hubble Atlas of Galaxies, Washington: Carnegie Institution, 1961 These bulges are composed primarily of stars that are older, Population II stars, and hence have a reddish hue (see stellar evolution).
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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 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.
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NGC 1375 is an early-type galaxy with a Hubble classification of SB0 pec, indicating it is a barred lenticular galaxy. Despite their name, early-type galaxies are much older than spiral galaxies, and mostly comprise old, red-colored stars. Very little star formation occurs in these galaxies; the lack of star formation in elliptical galaxies appears to start at the center and then slowly propagates outward. This is an early-type lenticular galaxy, with similar nature as early-type ellipticals.
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NGC 7243 is an open cluster 2500 light-years from Earth, visible in small amateur telescopes. It has a few dozen "scattered" stars, the brightest of which are of the 8th magnitude. BL Lacertae is the prototype of the BL Lacertae objects, which appear to be dim variable stars but are actually the variable nuclei of elliptical galaxies; they are similar to quasars. It lent its name to a whole type of celestial objects, the BL Lacertae objects (a subtype of blazar).
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But the lines in the stars of Oosterhoff type I (Oo I) cluster are not quite as weak as those in type II (Oo II). Hence type I are referred to as "metal-rich" (for example, Terzan 7), while type II are "metal- poor" (for example, ESO 280-SC06). These two populations have been observed in many galaxies, especially massive elliptical galaxies. Both groups are nearly as old as the universe itself and are of similar ages, but differ in their metal abundances.
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The galaxy is relatively small: it is a dwarf galaxy, a type of galaxy much smaller than normal spiral galaxies and elliptical galaxies. In fact, it is only 11000 light years (3300 parsecs) wide at its widest; our own galaxy, Milky Way, in comparison, is about ten times larger. Dwarf galaxies like these usually have about a billion stars. NGC 5264 also is relatively blue-coloured; this is from it interacting with other galaxies, supplying it with gas for star formation.
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The number of stars in any small patch of a galaxy will vary from point to point, creating a noise-like fluctuation in its surface brightness. While the various stars present in a galaxy will cover an enormous range of luminosity, the SBF can be characterized as having an average brightness. A galaxy twice as far away appears twice as smooth as a result of the averaging. Older elliptical galaxies have fairly consistent stellar populations, thus it closely approximates a standard candle.
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The amplitude of the spectrum gives the luminosity of the fluctuation star. Because the technique depends on a precise understanding of the image structure of the galaxy, extraneous sources such as globular clusters and background galaxies must be excluded. Corrections for interstellar dust absorption must also be accounted. In practice this means that SBF works best for elliptical galaxies or the bulges of S0 galaxies, and less so for spiral galaxies as they generally have complex morphologies and extensive dust features.
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These galaxies contain little or no interstellar dust, few star-forming regions, and older stars. Elliptical galaxies are more commonly found at the core of galactic clusters, and may have been formed through mergers of large galaxies. A spiral galaxy is organized into a flat, rotating disk, usually with a prominent bulge or bar at the center, and trailing bright arms that spiral outward. The arms are dusty regions of star formation within which massive young stars produce a blue tint.
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She was responsible for the selection of music on the Voyager Golden Record for the Voyager 1 and Voyager 2 exploratory missions. Druyan also sponsored the Cosmos 1 spacecraft. Gertrude B. Elion was an American biochemist and pharmacologist, awarded the Nobel Prize in Physiology or Medicine in 1988 for her work on the differences in biochemistry between normal human cells and pathogens. Sandra Moore Faber, with Robert Jackson, discovered the Faber–Jackson relation between luminosity and stellar dispersion velocity in elliptical galaxies.
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O type main-sequence stars and the most massive of the B type blue-white stars become supergiants. Due to their extreme masses, they have short lifespans, between 30 million years and a few hundred thousand years. They are mainly observed in young galactic structures such as open clusters, the arms of spiral galaxies, and in irregular galaxies. They are less abundant in spiral galaxy bulges and are rarely observed in elliptical galaxies, or globular clusters, which are composed mainly of old stars.
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It is believed that giant elliptical galaxies form when spirals and irregular galaxies collide. The wealth of galaxies at different stages of their evolution also allowed astronomers to estimate the variation in the rate of star formation over the lifetime of the Universe. While estimates of the redshifts of HDF galaxies are somewhat crude, astronomers believe that star formation was occurring at its maximum rate 8–10 billion years ago, and has decreased by a factor of about 10 since then.Connolly et al.
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For example, when two disk galaxies collide they begin with their stars in a orderly rotation in the planes of the two separate disks. During the merger, that ordered motion is transformed into random energy (“thermalized”). The resultant galaxy is dominated by stars that orbit the galaxy in a complicated and random interacting network of orbits, which is what is observed in elliptical galaxies. NGC 3921 is an interacting pair of disc galaxies in the late stages of its merger.
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A dwarf spheroidal galaxy (dSph) is a term in astronomy applied to small, low- luminosity galaxies with very little dust and an older stellar population. They are found in the Local Group as companions to the Milky Way and to systems that are companions to the Andromeda Galaxy (M31). While similar to dwarf elliptical galaxies in appearance and properties such as little to no gas or dust or recent star formation, they are approximately spheroidal in shape and generally have lower luminosity.
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In the case of SN 2011fe, the companion star must have been smaller than the Sun, if it existed. The Chandra X-ray Observatory revealed that the X-ray radiation of five elliptical galaxies and the bulge of the Andromeda Galaxy is 30–50 times fainter than expected. X-ray radiation should be emitted by the accretion discs of Type Ia supernova progenitors. The missing radiation indicates that few white dwarfs possess accretion discs, ruling out the common, accretion-based model of Ia supernovae.
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These galaxies are often fit by a Sérsic model with an added central component representing the nucleus. A. Graham & R. Guzmán (2003), HST Photometry of Dwarf Elliptical Galaxies in Coma P. Cote et al. (2006), The ACS Virgo Cluster Survey. VIII. The Nuclei of Early-Type Galaxies The Einasto profile is mathematically identical to the Sérsic profile, except that I is replaced by \rho, the volume density, and R is replaced by r, the internal (not projected on the sky) distance from the center.
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Astronomers posit that its dust lanes, not common in elliptical galaxies, are due to a previous merger with another galaxy, probably a spiral galaxy. NGC 5128 appears in the optical spectrum as a fairly large elliptical galaxy with a prominent dust lane. Its overall magnitude is 7.0 and it has been seen under perfect conditions with the naked eye, making it one of the most distant objects visible to the unaided observer. In equatorial and southern latitudes, it is easily found by star hopping from Omega Centauri.
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Its size on night sky is 2.6' x 2.5' which is, combined with the estimated distance, proportional to real size of 50,000 light-years. Despite their name, early-type galaxies are much older than spiral galaxies, and mostly comprise old, red-colored stars. Very little star formation occurs in these galaxies; the lack of star formation in elliptical galaxies appears to start at the center and then slowly propagates outward. It is rich with globular cluster, with an estimated number of cluster of 406 ± 81.
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Arp realized that the reason why galaxies formed into spiral or elliptical shapes was not well understood. He perceived peculiar galaxies as small "experiments" that astronomers could use to understand the physical processes that distort spiral or elliptical galaxies. With this atlas, astronomers had a sample of peculiar galaxies that they could study in more detail. The atlas does not present a complete overview of every peculiar galaxy in the sky but instead provides examples of the different phenomena as observed in nearby galaxies.
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Ultra-compact dwarf galaxies (UCD) are a class of very compact galaxies with very high stellar densities, discovered in the 2000s. They are thought to be on the order of 200 light years across, containing about 100 million stars.Anglo- Australian Observatory Astronomers discover dozens of mini-galaxies 0100 AEST Friday 2 April 2004. It is theorised that these are the cores of nucleated dwarf elliptical galaxies that have been stripped of gas and outlying stars by tidal interactions, travelling through the hearts of rich clusters.
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Short gamma-ray bursts appear to be an exception. Until 2007, only a handful of these events have been localized to a definite galactic host. However, those that have been localized appear to show significant differences from the long-burst population. While at least one short burst has been found in the star-forming central region of a galaxy, several others have been associated with the outer regions and even the outer halo of large elliptical galaxies in which star formation has nearly ceased.
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X-ray observations by the Chandra X-ray Observatory revealed six sources in the HDF, which were found to correspond to three elliptical galaxies, one spiral galaxy, one active galactic nucleus and one extremely red object, thought to be a distant galaxy containing a large amount of dust absorbing its blue light emissions.Hornschemeier et al. (2000) Ground-based radio images taken using the VLA revealed seven radio sources in the HDF, all of which correspond to galaxies visible in the optical images.Kellerman et al.
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IC 2006 is an early-type galaxy with a Hubble classification of E1, but has also been listed as a lenticular galaxy with a morphological type of SA0−. Despite their name, early-type galaxies are much older than spiral galaxies, and mostly comprise old, red- colored stars. Very little star formation occurs in these galaxies; the lack of star formation in elliptical galaxies appears to start at the center and then slowly propagates outward. Its age is estimated to be 8.1 ± 1.7 billion years.
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The diffuse stellar halo extends out to one million light years in diameter. Orbiting the galaxy is a very large population of globular clusters. NGC 4889 is also a strong source of soft X-ray, ultraviolet, and radio frequency radiation. As the largest and the most massive galaxy easily visible to Earth, NGC 4889 has played an important role in both amateur and professional astronomy, and has become a prototype in studying the dynamical evolution of other supergiant elliptical galaxies in the more distant universe.
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The giant elliptical galaxy ESO 325-G004 An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the three main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work The Realm of the Nebulae, Alt URL(pp. 124–151) along with spiral and lenticular galaxies. Elliptical (E) galaxies are, together with lenticular galaxies (S0) with their large-scale disks, and ES galaxiesLiller, M.H. (1966), The Distribution of Intensity in Elliptical Galaxies of the Virgo Cluster.
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Antlia is classified as a rare Bautz–Morgan type III cluster, meaning it has no central dominant (cD) brightest cluster galaxy. However, the cluster is dominated by two massive elliptical galaxies, NGC 3268 and NGC 3258, and contains a total of about 234 galaxies. The cluster is very dense compared to other clusters such as Virgo and Fornax, thus containing early-type galaxies and a larger portion of dwarf ellipticals. The cluster is split into two galaxy groups, the Northern subgroup gravitating around NGC 3268, and the Southern subgroup centered on NGC 3258.
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Star formation in what are now "dead" galaxies sputtered out billions of years ago. One observation (see above) that must be explained by a successful theory of galaxy evolution is the existence of two different populations of galaxies on the galaxy color-magnitude diagram. Most galaxies tend to fall into two separate locations on this diagram: a "red sequence" and a "blue cloud". Red sequence galaxies are generally non-star-forming elliptical galaxies with little gas and dust, while blue cloud galaxies tend to be dusty star-forming spiral galaxies.
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NGC 3923 Elliptical Shell Galaxy (Hubble photograph) A shell galaxy is a type of elliptical galaxy where the stars in the galaxy's halo are arranged in concentric shells. About one-tenth of elliptical galaxies have a shell-like structure, which has never been observed in spiral galaxies. The shell-like structures are thought to develop when a larger galaxy absorbs a smaller companion galaxy. As the two galaxy centers approach, the centers start to oscillate around a center point, the oscillation creates gravitational ripples forming the shells of stars, similar to ripples spreading on water.
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The type-cD galaxySidereal Times, June 2002, page 3 (also cD-type galaxy,Proceedings of PATRAS 2008, page 59 cD galaxyGalaxy Clusters, Jan Hartlap, page 3) is a galaxy morphology classification, a subtype of type-D giant elliptical galaxy. Characterized by a large halo of stars,Surface Photometry and the Structure of Elliptical Galaxies, "Chapter 11. cD and Brightest Cluster Galaxies", John Kormendy, S. Djorgovski, 1989 they can be found near the centres of some rich galaxy clusters.A Dictionary of Astronomy, "cD galaxy" (accessed 14 April 2010) They are also known as supergiant ellipticalsencyclopedia.
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Renán Arcadio Poveda Ricalde (born 15 July 1930) is a prominent Mexican astronomer who developed a method to calculate the mass of elliptical galaxies. He received Mexico's National Prize for Arts and Sciences in 1975, chaired its National Astronomical Observatory from 1968 to 1980 and was elected to The National College in 1989. Poveda was born in Mérida, Yucatán. He initially enrolled at the National Autonomous University of Mexico but ended up graduating with both a Bachelor of Arts degree (1953) and a PhD in Astronomy (1956) from the University of California, Berkeley.
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Large amounts of dark matter are necessary to prevent the gas from escaping the galaxy; the visible mass clearly is not large enough to hold such an extensive gas halo. The dark matter halo is estimated to have 10 times the mass of the stars in the galaxy. NGC 4555 is important because of its isolation. Most elliptical galaxies are found in the cores of groups and clusters of galaxies, and almost all those for which dark matter estimates are available are located in the centres of these larger systems.
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Charles Messier discovered Messier 58, along with the elliptical galaxies Messier 59 and Messier 60, on April 15, 1779. M58 was reported on the chart of the Comet of 1779 as it was almost on the same parallel as the star Epsilon Virginis. Messier described M58 as a very faint nebula in Virgo which would disappear in the slightest amount of light he used to illuminate the micrometer wires. This description was later contradicted by John Herschel's observations in 1833 where he described it as a very bright galaxy, especially towards the middle.
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The latest determination of the distance to Maffei 1, which is based on the re-calibrated luminosity/velocity dispersion relation for the elliptical galaxies and the updated extinction, is . The larger (≥3 Mpc) distances reported in the past 20 years would imply that Maffei 1 has never been close enough to the Local Group to significantly influence its dynamics. Maffei 1 moves away from the Sun at the speed of about 66 km/s. Its velocity relative to the Local Group's center of mass is, however, 297 km/s away.
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Artist's impression of the central bulge of the Milky Way. In astronomy, a galactic bulge (or simply bulge) is a tightly packed group of stars within a larger star formation. The term almost exclusively refers to the central group of stars found in most spiral galaxies (see galactic spheroid). Bulges were historically thought to be elliptical galaxies that happened to have a disk of stars around them, but high-resolution images using the Hubble Space Telescope have revealed that many bulges lie at the heart of a spiral galaxy.
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Sometimes bulges contain nuclear rings that are forming stars at much higher rate (per area) than is typically found in outer disks, as shown in NGC 4314 (see photo). A Hubble Space Telescope image of the central region of NGC 4314, a galaxy with a star- forming nuclear ring. Properties such as spiral structure and young stars suggest that some bulges did not form through the same process that made elliptical galaxies and classical bulges. Yet the theories for the formation of pseudobulges are less certain than those for classical bulges.
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Though stars almost never get close enough to actually collide in galaxy mergers, giant molecular clouds rapidly fall to the center of the galaxy where they collide with other molecular clouds. These collisions then induce condensations of these clouds into new stars. We can see this phenomenon in merging galaxies in the nearby universe. Yet, this process was more pronounced during the mergers that formed most elliptical galaxies we see today, which likely occurred 1–10 billion years ago, when there was much more gas (and thus more molecular clouds) in galaxies.
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Mergers can be categorized by the degree to which the gas (if any) carried within and around the merging galaxies interacts: ;Wet merger: A wet merger is between gas-rich galaxies ("blue" galaxies). Wet mergers typically produce a large amount of star formation, transform disc galaxies into elliptical galaxies and trigger quasar activity. ;Dry merger: A merger between gas-poor galaxies ("red" galaxies) is called dry. Dry mergers typically do not greatly change the galaxies' star formation rates, but can play an important role in increasing stellar mass.
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NGC 185 was first photographed between 1898 and 1900 by James Edward Keeler with the Crossley Reflector of Lick Observatory. Unlike most dwarf elliptical galaxies, NGC 185 contains young stellar clusters, and star formation proceeded at a low rate until the recent past. NGC 185 has an active galactic nucleus (AGN) and is usually classified as a type 2 Seyfert galaxy, though its status as a Seyfert is questioned. It is possibly the closest Seyfert galaxy to Earth, and is the only known Seyfert in the Local Group.
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Minor galactic mergers involve two galaxies of very different masses, and are not limited to giant ellipticals. The Milky Way galaxy, depending upon an unknown tangential component, is on a four- to five-billion-year collision course with the Andromeda Galaxy.Nagamine, Kentaro; Loeb, Abraham (2003), Future evolution of nearby large-scale structures in a universe dominated by a cosmological constant It has been theorized that an elliptical galaxy will result from a merger of the two spirals. It is believed that black holes may play an important role in limiting the growth of elliptical galaxies in the early universe by inhibiting star formation.
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However, it is also hypothesized that any hydrogen- stripped Type Ib or Ic supernova could be a GRB, dependent upon the geometry of the explosion. In any case, astronomers believe that most Type Ib, and probably Type Ic as well, result from core collapse in stripped, massive stars, rather than from the thermonuclear runaway of white dwarfs. As they are formed from rare, very massive stars, the rate of Type Ib and Ic supernovae occurrence is much lower than the corresponding rate for Type II supernovae. They normally occur in regions of new star formation, and are extremely rare in elliptical galaxies.
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There are many types of galaxy mergers, which do not necessarily result in elliptical galaxies, but result in a structural change. For example, a minor merger event is thought to be occurring between the Milky Way and the Magellanic Clouds. Mergers between such large galaxies are regarded as violent, and the frictional interaction of the gas between the two galaxies can cause gravitational shock waves, which are capable of forming new stars in the new elliptical galaxy. By sequencing several images of different galactic collisions, one can observe the timeline of two spiral galaxies merging into a single elliptical galaxy.
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Such merger events may have fueled the central supermassive black hole, that has a mass estimated in 130-150 million of solar masses with gas, causing the galaxy to become a radio galaxy. He also states that NGC 1316 is comparable to the giant elliptical galaxies found in the centers of other clusters of galaxies. Using spectroscopy of its brightest globular clusters, the merger is estimated to have occurred ~3 billion years ago. It has been proposed too that NGC 1316 may be a galaxy in evolution that eventually will become a Sombrero-like system dominated by a large bulge.
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Some giant elliptical galaxies (particularly those at the centers of galaxy clusters), such as M87, have as many as 13,000 globular clusters. Every galaxy of sufficient mass in the Local Group has an associated group of globular clusters, and almost every large galaxy surveyed has been found to possess a system of globular clusters. The Sagittarius Dwarf galaxy, and the disputed Canis Major Dwarf galaxy appear to be in the process of donating their associated globular clusters (such as Palomar 12) to the Milky Way. This demonstrates how many of this galaxy's globular clusters might have been acquired in the past.
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A central velocity dispersion refers to the σ of the interior regions of an extended object, such as a galaxy or cluster. The relationship between velocity dispersion and matter (or the observed electromagnetic radiation emitted by this matter) takes several forms in astronomy based on the object(s) being observed. For instance, the M–σ relation was found for material circling black holes, the Faber–Jackson relation for elliptical galaxies, and the Tully–Fisher relation for spiral galaxies. For example, the σ found for objects about the Milky Way's supermassive black hole (SMBH) is about 75 km/s.
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Tod R. Lauer (born 1957) is an American astronomer on the research staff of the National Optical Astronomy Observatory. He was a member of the Hubble Space Telescope Wide Field and Planetary Camera team, and is a founding member of the Nuker Team. His research interests includes observational searches for massive black holes in the centers of galaxies, the structure of elliptical galaxies, stellar populations, large-scale structure of the universe, and astronomical image processing. He was the Principal Investigator of the Destiny JDEM concept study, one of the precursors to the Wide Field Infrared Survey Telescope mission.
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1ES 1101-232 is an active galactic nucleus of a distant galaxy known as a blazar. An X-ray source (catalogued as A 1059-22) was first recorded by Maccagni and colleagues in a 1978 paper; they thought the source arose from a galaxy in the Abell 1146 galaxy cluster, which contained many giant elliptical galaxies. In 1989, Remillard and colleagues linked the X-ray source with a visual object and established that the object was surrounded by a large elliptical galaxy. They also discovered that the object (and galaxy) were more distant, with a redshift of 0.186.
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Based on the method of comparing the luminosities of globular clusters (located in galactic halos) from distant galaxies to that of the Virgo Cluster, the globular cluster luminosity function carries an uncertainty of distance of about 20% (or 0.4 magnitudes). US astronomer William Alvin Baum first attempted to use globular clusters to measure distant elliptical galaxies. He compared the brightest globular clusters in Virgo A galaxy with those in Andromeda, assuming the luminosities of the clusters were the same in both. Knowing the distance to Andromeda, Baum has assumed a direct correlation and estimated Virgo A's distance.
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Cepheids in particular are massive stars, with short lifetimes, so they will only be found in places where stars have very recently been formed. Consequently, because elliptical galaxies usually have long ceased to have large-scale star formation, they will not have Cepheids. Instead, distance indicators whose origins are in an older stellar population (like novae and RR Lyrae variables) must be used. However, RR Lyrae variables are less luminous than Cepheids, and novae are unpredictable and an intensive monitoring program—and luck during that program—is needed to gather enough novae in the target galaxy for a good distance estimate.
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2MASX J16270254+4328340 galaxy has merged with another galaxy leaving a fine mist, made of millions of stars, spewing from it in long trails. Galactic cannibalism refers to the process in which a large galaxy, through tidal gravitational interactions with a companion, merges with that companion; that results in a larger, often irregular galaxy. The most common result of the gravitational merger between two or more galaxies is an irregular galaxy, but elliptical galaxies may also result. It has been suggested that galactic cannibalism is currently occurring between the Milky Way and the Large and Small Magellanic Clouds.
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The galaxy product of the collision has been nicknamed Milkomeda or Milkdromeda. According to simulations, this object will look like a giant elliptical galaxy, but with a centre showing less stellar density than current elliptical galaxies. It is, however, possible the resulting object will be a large lenticular galaxy, depending on the amount of remaining gas in the Milky Way and Andromeda. In the far future, roughly 150 billion years from now, the remaining galaxies of the Local Group will coalesce into this object, that being the next evolutionary stage of the local group of galaxies.
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Elliptical galaxy NGC 4889 in front of hundreds of background galaxies. Giant elliptical galaxies like NGC 4889 are believed to be the result of multiple mergers of smaller galaxies. There is now little dust remaining to form the diffuse nebulae where new stars are created, so the stellar population is dominated by old, population II stars that contain relatively low abundances of elements other than hydrogen and helium. The egg- like shape of this galaxy is maintained by random orbital motions of its member stars, in contrast to the more orderly rotational motions found in a spiral galaxy such as the Milky Way.
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Mainstream astronomical theory before Galaxy Zoo held that elliptical (or 'early type') galaxies were red in color and spiral (or 'late type') galaxies were blue in color: several papers published as a result of Galaxy Zoo have proved otherwise. A population of blue ellipticals was found. These are galaxies which have changed their shape from spiral to oval, but still have young stars in them. Indeed, Galaxy Zoo came about through Schawinski's searching for blue elliptical galaxies, as near the end of 2006, he had spent most of his waking hours trying to find these rare galaxies.
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Also, away from the center of the galaxy gas clouds will run into each other producing shocks which stimulate the formation of new stars in gas clouds. The result of all this violence is that galaxies tend to have little gas available to form new stars after they merge. Thus if a galaxy is involved in a major merger, and then a few billion years pass, the galaxy will have very few young stars (see Stellar evolution) left. This is what we see in today's elliptical galaxies, very little molecular gas and very few young stars.
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Independently, Lacey and Cole showed at the same 1992 conference how they used the Press–Schechter formalism combined with dynamical friction to statistically generate Monte Carlo realisations of dark matter halo merger history trees and the corresponding formation of the stellar cores (galaxies) of the haloes. Kauffmann, White and Guiderdoni extended this approach in 1993 to include semi-analytical formulae for gas cooling, star formation, gas reheating from supernovae, and for the hypothesised conversion of disc galaxies into elliptical galaxies. Both the Kauffmann group and Okamoto and Nagashima later took up the N-body simulation derived merger history tree approach.
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Sparke was born in London, and read mathematics as an undergraduate at the University of Cambridge. She completed a Ph.D. in astronomy in 1981 from the University of California, Berkeley; her dissertation was Swirling Gas Flows in Elliptical Galaxies. After postdoctoral research at the Institute for Advanced Study, the University of Cambridge, and the Kapteyn Astronomical Institute, she became a faculty member at the University of Wisconsin–Madison. She retired in 2010 to become a professor emeritus, served as a program manager at the National Science Foundation for two years, and became research program manager in astrophysics at NASA and later Explorers Program Scientist at NASA.
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Together with his student Ido Finkelman, and with colleagues from Russia and the Netherlands, they showed that the visible ring is part of an even larger ring of neutral hydrogen and proposed that the ring represents material accreted by the elliptical core at least one billion years ago. Hoag's Object would, therefore, represent a much undisturbed galaxy . Brosch and colleagues, and other students, investigated the properties of extragalactic dust by concentrating on elliptical galaxies with dark lanes. Modeling the light distribution of the unaffected parts of a galaxy, and subtracting from it the detected light distribution, they derived the amount of light missing because of the dust obscuration.
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Observation of giant stars in the halo indicate there are two general populations: a dominant metal-rich subpopulation and a weaker metal-poor group. Messier 105 is known to have a supermassive black hole at its core whose mass is estimated to be between and . The galaxy has a weak active galactic nucleus of the LINER type with a spectral class of L2/T2, meaning no broad Hα line and intermediate emission line ratios between a LINER and a H II region. The galaxy also contains a few young stars and stellar clusters, suggesting some elliptical galaxies still form new stars, but very slowly.
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Since then, several dozen short gamma- ray burst afterglows have been detected and localized, several of which are associated with regions of little or no star formation, such as large elliptical galaxies and the central regions of large galaxy clusters.Bloom 2006Hjorth 2005Berger 2007Gehrels 2005 This rules out a link to massive stars, confirming that short events are physically distinct from long events. In addition, there has been no association with supernovae.Zhang 2009 The true nature of these objects was initially unknown, and the leading hypothesis was that they originated from the mergers of binary neutron starsNakar 2007 or a neutron star with a black hole.
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Red dwarf starsThe term dwarf applies to all stars in the main sequence, including the Sun. are the smallest, coolest, and most common type of star. Estimates of their abundance range from 70% of stars in spiral galaxies to more than 90% of all stars in elliptical galaxies, an often quoted median figure being 73% of the stars in the Milky Way (known since the 1990s from radio telescopic observation to be a barred spiral).Dole, Stephen H. Habitable Planets for Man 1965 Rand Corporation report, published in book form--A figure of 73% is given for the percentage of red dwarfs in the Milky Way.
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Abell 2744 galaxy cluster - Hubble Frontier Fields view (7 January 2014). Abell 383, the giant cluster of elliptical galaxies in the centre of this image, contains so great a mass of dark matter that its gravity bends the light from a background object into an arc, a phenomenon known as strong gravitational lensing. The Abell catalogue is a catalogue of approximately 4,000 galaxy clusters with at least 30 members, almost complete to a redshift of z = 0.2. It was originally compiled by the American astronomer George O. Abell in 1958 using plates from POSS, and extended to the southern hemisphere by Abell, Corwin and Olowin in 1987.
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In 1983 this estimate was revised up to 2.1 Mpc by Ronald Buta and Marshall McCall using the general relation between the luminosity and velocity dispersion for elliptical galaxies. That distance puts Maffei 1 well outside the Local Group, but close enough to have influenced it in the past. In 1993 Gerard Luppino and John Tonry used surface brightness fluctuations to derive a new distance estimate to Maffei 1 of . Later in 2001, Tim Davidge and Sidney van den Bergh used adaptive optics to observe the brightest asymptotic giant branch stars in Maffei 1 and concluded that it is located at the distance 4.4 Mpc from the Sun.
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In 2018 the discovery was announced of a very low surface brightness galaxy near Epsilon Antliae, Antlia 2, which is a satellite galaxy of the Milky Way. The Antlia Cluster, also known as Abell S0636, is a cluster of galaxies located in the Hydra-Centaurus Supercluster. It is the third nearest to the Local Group after the Virgo Cluster and the Fornax Cluster. The cluster's distance from earth is to Located in the southeastern corner of the constellation, it boasts the giant elliptical galaxies NGC 3268 and NGC 3258 as the main members of a southern and northern subgroup respectively, and contains around 234 galaxies in total.
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Using data drawn from the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) and TIFR GMRT Sky Survey (TGSS), they investigate the most powerful radio sources, namely the largest elliptical galaxies emitting plasma-filled jets. The abstract begins: "We study the mutual alignment of radio sources within two surveys, FIRST and TGSS. This is done by producing two position angle catalogues containing the preferential directions of respectively 30059 and 11674 extended sources distributed over more than 7000 and 17000 square degrees." The FIRST sample sources were identified by participants in RGZ, while the TGSS sample was the result of an automated process.
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It is thought that this is because elliptical galaxies are the end products of major mergers which use up the majority of gas during the merger, and thus further star formation after the merger is quenched. Galaxy mergers can be simulated in computers, to learn more about galaxy formation. Galaxy pairs initially of any morphological type can be followed, taking into account all gravitational forces, and also the hydrodynamics and dissipation of the interstellar gas, the star formation out of the gas, and the energy and mass released back in the interstellar medium by supernovae. Such a library of galaxy merger simulations can be found on the GALMER website.
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In the end, supernova explosions and strong stellar winds from the most massive stars in the resulting star cluster will disperse the gases of the H II region, leaving behind a cluster of stars which have formed, such as the Pleiades. H II regions can be observed at considerable distances in the universe, and the study of extragalactic H II regions is important in determining the distance and chemical composition of galaxies. Spiral and irregular galaxies contain many H II regions, while elliptical galaxies are almost devoid of them. In spiral galaxies, including our Milky Way, H II regions are concentrated in the spiral arms, while in irregular galaxies they are distributed chaotically.
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Universe Today, "What is the Largest Galaxy?", Fraser Cain (accessed 14 April 2010)EurekAlert, "Scientists observe largest explosion in space", Andrea Gibson, 5 January 2005 (accessed 15 April 2010) cD galaxies are similar to lenticular galaxies (S0) or elliptical galaxies (E#), but many times larger, some having envelopes that exceed one million light years in radius.Encyclopædia Britannica, "cD-galaxy" (accessed 14 April 2010) They appear elliptical-like, with large low surface brightness envelopes which may belong as much to the galaxy cluster as the cD galaxy. It is currently thought that cDs are the result of galaxy mergers.COSMOS - The SAO Encyclopedia of Astronomy, "CD Galaxies", Swinburne University of Technology (accessed 14 April 2010) Some cDs have multiple galactic nuclei.
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There exists a class of 'radiatively inefficient' solutions to the equations that govern accretion. The most widely known of these is the Advection Dominated Accretion Flow (ADAF), but other theories exist. In this type of accretion, which is important for accretion rates well below the Eddington limit, the accreting matter does not form a thin disc and consequently does not efficiently radiate away the energy that it acquired as it moved close to the black hole. Radiatively inefficient accretion has been used to explain the lack of strong AGN-type radiation from massive black holes at the centres of elliptical galaxies in clusters, where otherwise we might expect high accretion rates and correspondingly high luminosities.
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There is strong evidence that some short-duration gamma-ray bursts occur in systems with no star formation and no massive stars, such as elliptical galaxies and galaxy halos. The favored theory for the origin of most short gamma-ray bursts is the merger of a binary system consisting of two neutron stars. According to this model, the two stars in a binary slowly spiral towards each other because gravitational radiation releases energyAbbott 2007Kochanek 1993 until tidal forces suddenly rip the neutron stars apart and they collapse into a single black hole. The infall of matter into the new black hole produces an accretion disk and releases a burst of energy, analogous to the collapsar model.
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X-ray jet made from a supermassive black hole found by NASA's Chandra X-ray Observatory, made visible by light from the early Universe X-ray astronomy uses X-ray wavelengths. Typically, X-ray radiation is produced by synchrotron emission (the result of electrons orbiting magnetic field lines), thermal emission from thin gases above 107 (10 million) kelvins, and thermal emission from thick gases above 107 Kelvin. Since X-rays are absorbed by the Earth's atmosphere, all X-ray observations must be performed from high-altitude balloons, rockets, or X-ray astronomy satellites. Notable X-ray sources include X-ray binaries, pulsars, supernova remnants, elliptical galaxies, clusters of galaxies, and active galactic nuclei.
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The cluster is a fairly heterogeneous mixture of spirals and ellipticals. , it is believed that the spiral galaxies of the cluster are distributed in an oblong prolate filament, approximately 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 aggregate of at least three separate subclumps: Virgo A, centered on M87, a second centered on the galaxy M86, and Virgo B, centered on M49, with some authors including a Virgo C subcluster, centered on the galaxy M60 as well as a LVC (Low Velocity Cloud) subclump, centered on the large spiral galaxy NGC 4216.
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Spiral galaxies, like the Milky Way, produce new generations of stars as long as they have dense molecular clouds of interstellar hydrogen in their spiral arms. Elliptical galaxies are largely devoid of this gas, and so form few new stars. The supply of star-forming material is finite; once stars have converted the available supply of hydrogen into heavier elements, new star formation will come to an end. The current era of star formation is expected to continue for up to one hundred billion years, and then the "stellar age" will wind down after about ten trillion to one hundred trillion years (1013–1014 years), as the smallest, longest-lived stars in our universe, tiny red dwarfs, begin to fade.
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Since the black hole at the center of the HCSS is essentially invisible, an HCSS would look very similar to a faint cluster of stars. Determining that an observed star cluster is a HCSS requires measuring the orbital velocities of the stars in the cluster via their Doppler shifts and verifying that they are moving much faster than expected for stars in an ordinary star cluster. This is a challenging observation to make because an HCSS would be relatively faint, requiring many hours of exposure time even on a 10m class telescope. The most promising places to look for HCSSs are cluster of galaxies, for two reasons: first, most of the galaxies in a galaxy cluster are elliptical galaxies which are believed to have formed through mergers.
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Some of the earliest detected radio sources are nearby active elliptical galaxies such as Messier 87 and Centaurus A. Another radio source, Cygnus A, was identified by Walter Baade and Rudolph Minkowski as a tidally distorted galaxy with an unusual emission-line spectrum, having a recessional velocity of 16,700 kilometers per second. The 3C radio survey led to further progress in discovery of new radio sources as well as identifying the visible-light sources associated with the radio emission. In photographic images, some of these objects were nearly point-like or quasi-stellar in appearance, and were classified as quasi-stellar radio sources (later abbreviated as "quasars"). Soviet Armenian astrophysicist Viktor Ambartsumian introduced Active Galactic Nuclei in the early 1950s.
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Abraham's career has been notable for his contributions via non-parametric statistics to galaxy morphological classification, especially at high-redshift and early work on the Hubble Deep Field.Galaxy morphology to I=25 mag in the Hubble Deep Field, 1996, MNRAS, 279 L47 He was one of the leaders of the "Gemini Deep Deep Survey"Gemini Observatory - the Gemini Deep Deep Survey which led to several notable results on early galaxies including the evolution of elliptical galaxies and why a lot of them appear so remarkably old.Casey Kazan; The early universe puzzle, The Daily Galaxy (June 15th 2011). He is currently a co-principal-investigator on the Dragonfly Telephoto Array telescope, which images ultra-low surface brightness galaxies at visible wavelengths of light.
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The galaxy shows an enhanced rate of star formation that may have been triggered by a collision with a dwarf galaxy, or by the gravitational interaction with its neighbor compressing gas and dust. It was discovered by Friedrich August Theodor Winnecke in 1876. In the Atlas of Peculiar Galaxies, the galaxy is mentioned twice, once as Arp 25, in the category spiral galaxies with one heavy arm, and one more time as Arp 114, in the category elliptical galaxies close to and perturbing spiral galaxies, in pair with NGC 2300. NGC 2276 has been home to six supernovae in the last 60 years; SN 1962Q (mag 16.9), SN 1968V (mag 15.7), SN 1968W (mag 16.6), SN 1993X (type II, mag.
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Hubble complimented Mayall for his work, although significant results were never achieved (nor by Hubble either) due to the lack of accurate magnitude standards for the faint galaxies that were measured and by the (then unrealized) very strong tendency of galaxies to cluster. While working on his thesis, Mayall had an idea of designing a small, fast slitless spectrograph, optimized for nebulae and galaxies. He believed that if it were used in conjunction with the Crossley reflector it would make that facility competitive for at least some of the work that Humason and Hubble were doing with the larger Mt. Wilson telescopes. It was never expected to compete with the Mt. Wilson instrument for stars or elliptical galaxies, which have condensed and relatively bright nuclei.
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Velocity dispersion (y-axis) plotted against absolute magnitude (x-axis) for a sample of elliptical galaxies, with the Faber–Jackson relation shown in blue. The Faber–Jackson relation provided the first empirical power-law relation between the luminosity L and the central stellar velocity dispersion \sigma of elliptical galaxy, and was presented by the astronomers Sandra M. Faber and Robert Earl Jackson in 1976. Their relation can be expressed mathematically as: : L \propto \sigma^ \gamma with the index \gamma approximately equal to 4. In 1962, Rudolph Minkowski had discovered and wrote that a "correlation between velocity dispersion and [luminosity] exists, but it is poor" and that "it seems important to extend the observations to more objects, especially at low and medium absolute magnitudes".
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Open clusters are not seen in elliptical galaxies: star formation ceased many millions of years ago in ellipticals, and so the open clusters which were originally present have long since dispersed. In our galaxy, the distribution of clusters depends on age, with older clusters being preferentially found at greater distances from the galactic centre, generally at substantial distances above or below the galactic plane. Tidal forces are stronger nearer the centre of the galaxy, increasing the rate of disruption of clusters, and also the giant molecular clouds which cause the disruption of clusters are concentrated towards the inner regions of the galaxy, so clusters in the inner regions of the galaxy tend to get dispersed at a younger age than their counterparts in the outer regions.
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Davies took his first degree in Physics at University College London and his PhD at the Institute of Astronomy and Churchill College, Cambridge. Posts at Lick Observatory, California, then Cambridge and Kitt Peak National Observatory, Arizona, followed. While at Kitt Peak he became part of the Seven Samurai collaboration which surveyed the distances and velocities of 400 nearby elliptical galaxies, discovering the Great Attractor, at that time thought to be pulling the Milky Way and other galaxies in the direction of the constellations of Hydra and Centaurus. Returning to the UK, Davies was based in Oxford leading the team that developed a proposal for UK participation in an 8-m telescope project which ultimately led to the establishment of the Gemini Observatory, twin 8m telescopes in Hawaii and Chile.
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The Andromeda Galaxy's two main companions, M32 and M110 (also known as NGC 221 and NGC 205, respectively) are faint elliptical galaxies that lie near it. M32, visible with a far smaller size of 8.7 by 6.4 arcminutes, compared to M110, appears superimposed on the larger galaxy in a telescopic view as a hazy smudge, M110 also appears slightly larger and distinct from the larger galaxy; M32 is 0.5° south of the core, M32 is 1° northwest of the core. M32 was discovered in 1749 by French astronomer Guillaume Le Gentil and has since been found to lie closer to Earth than the Andromeda Galaxy itself. It is viewable in binoculars from a dark site owing to its high surface brightness of 10.1 and overall magnitude of 9.0.
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Stephan's Quintet, a compact group of galaxies discovered about 130 years ago and located about 280 million light years from Earth, provides a rare opportunity to observe a galaxy group in the process of evolving from an X-ray faint system dominated by spiral galaxies to a more developed system dominated by elliptical galaxies and bright X-ray emission. Being able to witness the dramatic effect of collisions in causing this evolution is important for increasing our understanding of the origins of the hot, X-ray bright halos of gas in groups of galaxies. Stephan's Quintet are of interest because of their violent collisions. Four of the five galaxies in Stephan's Quintet form a physical association, and are involved in a cosmic dance that most likely will end with the galaxies merging.
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Like the Tully–Fisher relation, the Faber–Jackson relation provides a means of estimating the distance to a galaxy, which is otherwise hard to obtain, by relating it to more easily observable properties of the galaxy. In the case of elliptical galaxies, if one can measure the central stellar velocity dispersion, which can be done relatively easily by using spectroscopy to measure the Doppler shift of light emitted by the stars, then one can obtain an estimate of the true luminosity of the galaxy via the Faber–Jackson relation. This can be compared to the apparent magnitude of the galaxy, which provides an estimate of the distance modulus and, hence, the distance to the galaxy. By combining a galaxy's central velocity dispersion with measurements of its central surface brightness and radius parameter, it is possible to improve the estimate of the galaxy's distance even more.
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By convention, n is ten times the ellipticity of the galaxy, rounded to the nearest integer, where the ellipticity is defined as for an ellipse with semi-major and semi-minor axes of lengths a and b respectively. The ellipticity increases from left to right on the Hubble diagram, with near-circular (E0) galaxies situated on the very left of the diagram. It is important to note that the ellipticity of a galaxy on the sky is only indirectly related to the true 3-dimensional shape (for example, a flattened, discus-shaped galaxy can appear almost round if viewed face-on or highly elliptical if viewed edge-on). Observationally, the most flattened "elliptical" galaxies have ellipticities e = 0.7 (denoted E7). However, from studying the light profiles and the ellipticity profiles, rather than just looking at the images, it was realised in the 1960s that the E5–E7 galaxies are probably misclassified lenticular galaxies with large-scale disks seen at various inclinations to our line-of-sight.
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In contrast to star formation in density-wave theories, which are limited to disk-shaped galaxies and produce global spiral patterns, SSPSF applies equally well to spirals, to irregular galaxies and to any local concentrations of gas in elliptical galaxies. The effect may be envisioned as an "SIR infection model" in a differentially rotating disk, the host galaxy. The SIR model (perhaps most popularly familiar in the form of Conway's Game of Life) is applied to star formation propagating through the galaxy: Each generation of stars in a neighborhood includes some massive ones whose stellar winds and, soon, supernovae, produce shock waves in the gas (Susceptible material). These lead to collapsing nearby gas clouds, which produce the next generation of stars (Infection propagation); but in the immediate neighborhood, all initially available gas is used, so no further stars are born there for some period of time despite the shocks (Recovery from infection).
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