Elliptical galaxy - wikipedia Elliptical galaxy This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. Please help to improve this article by introducing more precise citations. ( March 2015 ) The giant elliptical galaxy ESO 325 - G004 An elliptical galaxy is a type of galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. Unlike flat spiral galaxies with organization and structure, they are more three - dimensional, without much structure, and their stars are in somewhat random orbits around the center. They are one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae, along with spiral and lenticular galaxies. Elliptical galaxies range in shape from nearly spherical to highly flat and 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. Stars found inside of elliptical galaxies are on average much older than stars found in spiral galaxies. Most elliptical galaxies are composed of older, low - mass stars, with a sparse interstellar medium and minimal star formation activity, and they tend to be surrounded by large numbers of globular clusters. Elliptical galaxies are believed to make up approximately 10 % -- 15 % of galaxies in the Virgo Supercluster, and they are not the dominant type of galaxy in the universe overall. They are preferentially found close to the centers of galaxy clusters. Elliptical galaxies are ( together with lenticular galaxies ) also called `` early - type '' galaxies ( ETG ), due to their location in the Hubble sequence, and are found to be less common in the early Universe. Contents 1 General characteristics 2 Star formation 3 Sizes and shapes 4 Evolution 5 Examples 6 See also 7 References 8 Further reading 9 External links General characteristics NGC 3597 is the product of a collision between two galaxies, and is slowly evolving to become a giant elliptical galaxy. 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. 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. The luminosity profiles of both elliptical galaxies and bulges are well fit by Sersic 's law. 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, via the M -- sigma relation which relates the velocity dispersion of the surrounding stars to the mass of the black hole at the center. Elliptical galaxies are preferentially found in galaxy clusters and in compact groups of galaxies. Star formation The traditional portrait 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. However, in recent years, evidence has shown that a reasonable proportion ( ~ 25 % ) of these galaxies have residual gas reservoirs and low level star - formation. Researchers with the Herschel Space Observatory have speculated that the central black holes in elliptical galaxies keep the gas from cooling enough for star formation. Sizes and shapes 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 10 to nearly 10 solar masses. This range is much broader for this galaxy type than for any other. The smallest, the dwarf elliptical galaxies, may be no larger than a typical globular cluster, but contain a considerable amount of dark matter not present in clusters. Most of these small galaxies may not be related to other ellipticals. The Hubble classification of elliptical galaxies contains an integer that describes how elongated the galaxy image is. The classification is determined by the ratio of the major ( a ) to the minor ( b ) axes of the galaxy 's isophotes : 10 × ( 1 − b a ) ( displaystyle 10 \times left ( 1 - ( \frac ( b ) ( a ) ) \right ) ) Thus for a spherical galaxy with a equal to b, the number is 0, and the Hubble type is E0. The limit is about E7, which is believed to be due to a bending instability that causes flatter galaxies to puff up. The most common shape is close to E3. Hubble recognized that his shape classification depends both on the intrinsic shape of the galaxy, as well as the angle with which the galaxy is observed. Hence, some galaxies with Hubble type E0 are actually elongated. There are two physical types of ellipticals ; the `` boxy '' giant ellipticals, whose shapes result from random motion which is greater in some directions than in others ( anisotropic random motion ), and the `` disky '' normal and low luminosity ellipticals, which have nearly isotropic random velocities but are flattened due to rotation. Dwarf elliptical galaxies have properties that are intermediate between those of regular elliptical galaxies and globular clusters. Dwarf spheroidal galaxies appear to be a distinct class : their properties are more similar to those of irregulars and late spiral - type galaxies. At the large end of the elliptical spectrum, there is further division, beyond Hubble classification. Beyond gE giant ellipticals, lies D - galaxies and cD - galaxies. These are similar to their smaller brethren, but more diffuse, with larger haloes. Some even appear more akin to lenticular galaxies. Evolution Elliptical galaxy IC 2006. It is widely accepted that the evolution of elliptical galaxies is primarily composed of the merging of smaller galaxies. Many galaxies in the universe are gravitationally bound to other galaxies, which means that they will never escape the pull of the other galaxy. If the galaxies are of similar size, the resultant galaxy will appear similar to neither of the two galaxies merging, but will instead be an elliptical galaxy. Such major galactic mergers are thought to have been common at early times, but may occur less frequently today. Minor galactic mergers involve two galaxies of very different masses, and are not limited to giant ellipticals. For example, our own Milky Way galaxy is merging with a couple of small galaxies right now. The Milky Way galaxy is also, depending upon an unknown tangential component, on a collision course in 4 -- 5 billion years with the Andromeda Galaxy. 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. Examples M32 M49 M59 M60 ( NGC 4649 ) M87 ( NGC 4486 ) M89 M105 ( NGC 3379 ) IC 1101, one of the largest galaxies in the observable universe. Maffei 1, the closest giant elliptical galaxy. Centaurus A ( NGC 5128 ), a radio galaxy, elliptical / lenticular disputed. See also Firehose instability Galaxy color -- magnitude diagram Galaxy morphological classification Hubble sequence Lenticular galaxy M -- sigma relation Osipkov -- Merritt model Sersic profile References Jump up ^ Hubble, E.P. ( 1936 ). The realm of the nebulae. Mrs. Hepsa Ely Silliman Memorial Lectures, 25. New Haven : Yale University Press. ISBN 9780300025002. OCLC 611263346. Archived from the original on 29 September 2012. ( pp. 124 -- 151 ) ^ Jump up to : John, D. ( 2006 ). Astronomy : The definitive guide to the universe. Bath, UK : Parragon Publishing., p. 224 - 225 Jump up ^ Loveday, J. ( February 1996 ). `` The APM Bright Galaxy Catalogue ''. Monthly Notices of the Royal Astronomical Society. 278 ( 4 ) : 1025 -- 1048. arXiv : astro - ph / 9603040. Bibcode : 1996MNRAS. 278.1025 L. doi : 10.1093 / mnras / 278.4. 1025. Jump up ^ Dressler, A. ( March 1980 ). `` Galaxy morphology in rich clusters -- Implications for the formation and evolution of galaxies ''. The Astrophysical Journal. 236 : 351 -- 365. Bibcode : 1980ApJ... 236... 351D. doi : 10.1086 / 157753. Jump up ^ Kormendy, John ; Ho, Luis C. ( 2013 - 08 - 18 ). `` Coevolution ( Or Not ) of Supermassive Black Holes and Host Galaxies ''. Annual Review of Astronomy and Astrophysics. 51 ( 1 ) : 511 -- 653. arXiv : 1304.7762. Bibcode : 2013ARA&A... 51... 511K. doi : 10.1146 / annurev - astro - 082708 - 101811. ISSN 0066 - 4146. Jump up ^ Young, L.M. ; et al. ( June 2011 ). `` The Atlas3D project -- IV : the molecular gas content of early - type galaxies ''. Monthly Notices of the Royal Astronomical Society. 414 ( 2 ) : 940 -- 967. arXiv : 1102.4633. Bibcode : 2011MNRAS. 414... 940Y. doi : 10.1111 / j. 1365 - 2966.2011. 18561. x. Jump up ^ Crocker, A.F. ; et al. ( January 2011 ). `` Molecular gas and star formation in early - type galaxies ''. Monthly Notices of the Royal Astronomical Society. 410 ( 2 ) : 1197 -- 1222. arXiv : 1007.4147. Bibcode : 2011MNRAS. 410.1197 C. doi : 10.1111 / j. 1365 - 2966.2010. 17537. x. Jump up ^ `` Red And Dead Galaxies Have Beating Black Hole ' Hearts ', Preventing Star Formation. '' Jump up ^ `` Galactic fireflies ''. ESA / Hubble Picture of the Week. Retrieved 13 February 2013. Jump up ^ Fraknoi, Andrew ; Morrison, David ; Wolf, Sidney C. ( 13 January 2017 ). Open Stax Astronomy. Retrieved 2 February 2017. Jump up ^ `` Elliptical galaxy IC 2006 ''. www.spacetelescope.org. ESA / Hubble. Retrieved 21 April 2015. Further reading Mo, Houjun ; van den Bosch, Frank ; White, Simon ( June 2010 ), Galaxy Formation and Evolution ( 1 ed. ), Cambridge University Press, ISBN 978 - 0521857932 External links Wikimedia Commons has media related to Elliptical galaxies. Elliptical Galaxies, SEDS Messier pages Elliptical Galaxies Galaxies Morphology Disc galaxy Lenticular galaxy barred unbarred Spiral galaxy Anemic galaxy barred flocculent grand design intermediate Magellanic unbarred Dwarf galaxy elliptical irregular spheroidal spiral Elliptical galaxy cD - galaxy Irregular galaxy barred Peculiar galaxy Ring galaxy Polar Structure Active galactic nucleus ( AGN ) Bar Bulge Dark matter halo Disc Galactic halo corona Galactic plane Interstellar medium Protogalaxy Spiral arm Supermassive black hole Active nuclei Blazar LINER Markarian galaxies Quasar Radio galaxy X-shaped Relativistic jet Seyfert galaxy Energetic galaxies LAE LIRG Starburst galaxy BCD Pea Hot, dust - obscured galaxies ( Hot DOGs ) Low activity LSB UDG Interaction Field galaxy Galactic tide Galaxy cloud Galaxy groups and clusters Galaxy group Galaxy cluster Brightest cluster galaxy Fossil galaxy group Interacting galaxy merger Jellyfish galaxy Satellite galaxy Stellar stream Superclusters Walls Void galaxy Voids and supervoids Lists Galaxies Galaxies named after people Largest Nearest Polar - ring galaxies Ring galaxies Spiral galaxies Groups and clusters Large quasar groups Quasars Superclusters Voids See also Dark galaxy Extragalactic astronomy Faint blue galaxy Galactic astronomy Galactic center Galactic coordinate system Galactic empire Galactic habitable zone Galactic magnetic fields Galactic orientation Galactic quadrant Galactic ridge Galaxy color -- magnitude diagram Galaxy formation and evolution Galaxy rotation curve Illustris project Intergalactic dust Intergalactic stars Intergalactic travel Population III stars Cosmos Redshift 7 galaxy Book Portal Retrieved from `` https://en.wikipedia.org/w/index.php?title=Elliptical_galaxy&oldid=829819167 '' Categories : Elliptical galaxies Galaxy morphological types Hidden categories : Use dmy dates from March 2017 Articles lacking in - text citations from March 2015 All articles lacking in - text citations All articles with unsourced statements Articles with unsourced statements from March 2015 Talk Contents Interaction About Wikipedia Afrikaans Asturianu Беларуская Беларуская ( тарашкевіца ) ‎ Български Bosanski Català Čeština Deutsch Eesti Ελληνικά Español Esperanto Euskara فارسی Français 한국어 हिन्दी Hrvatski Bahasa Indonesia Italiano עברית Кыргызча Lëtzebuergesch Lietuvių Magyar Македонски मराठी မြန်မာဘာသာ Nederlands 日本 語 Norsk Norsk nynorsk Occitan پنجابی Polski Português Română Русский Simple English Slovenčina Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska ไทย Türkçe Українська Tiếng Việt 中文 42 more Edit links This page was last edited on 11 March 2018, at 00 : 29. 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Question: what types of stars are found in elliptical galaxies
Answer: Most elliptical galaxies are composed of older, low-mass stars