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Dwarf galaxy

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TheLarge Magellanic Cloud,a satellite galaxy of theMilky Way

Adwarf galaxyis a smallgalaxycomposed of about 1000 up to several billionstars,as compared to theMilky Way's 200–400 billion stars.[1]TheLarge Magellanic Cloud,which closely orbits the Milky Way and contains over 30 billion stars,[2]is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition.

Formation

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Dwarf galaxies likeNGC 5264typically possess around a billion stars.[3]

One theory states that most galaxies, including dwarf galaxies, form in association withdark matter,or from gas that contains metals. However,NASA'sGalaxy Evolution Explorerspace probeidentified new dwarf galaxies forming out of gases with lowmetallicity.These galaxies were located in theLeo Ring,a cloud ofhydrogenandheliumaround two massive galaxies in theconstellationLeo.[4]

Because of their small size, dwarf galaxies have been observed being pulled toward andrippedby neighbouringspiral galaxies,resulting instellar streamsand eventuallygalaxy merger.[5]

Local dwarf galaxies

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ThePhoenix Dwarf Galaxyis a dwarf irregular galaxy, featuring younger stars in its inner regions and older ones at its outskirts.[6]

There are many dwarf galaxies in theLocal Group;these small galaxies frequently orbit larger galaxies, such as theMilky Way,theAndromeda Galaxyand theTriangulum Galaxy.A 2007 paper[7]has suggested that many dwarf galaxies were created bygalactic tidesduring the early evolutions of the Milky Way and Andromeda. Tidal dwarf galaxies are produced when galaxies collide and their gravitationalmasses interact.Streams of galactic material are pulled away from the parent galaxies and the halos ofdark matterthat surround them.[8]A 2018 study suggests that some local dwarf galaxies formed extremely early, during theDark Ageswithin the first billion years after theBig Bang.[9]

More than 20 known dwarf galaxies orbit the Milky Way, and recent observations[10]have also led astronomers to believe the largestglobular clusterin the Milky Way,Omega Centauri,is in fact the core of a dwarf galaxy with ablack holeat its centre, which was at some time absorbed by the Milky Way.

Common types

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UGC 11411is a galaxy known as an irregular blue compact dwarf (BCD) galaxy.[11]

Blue compact dwarf galaxies

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Blue compact dwarfPGC 51017.[13]

Inastronomy,ablue compact dwarf galaxy(BCD galaxy) is a small galaxy which contains largeclustersof young, hot, massivestars.These stars, the brightest of which are blue, cause the galaxy itself to appearbluein colour.[14]Most BCD galaxies are also classified as dwarfirregular galaxiesor as dwarflenticular galaxies.Because they are composed of star clusters, BCD galaxies lack a uniform shape. They consume gas intensely, which causes their stars to become very violent when forming.

BCD galaxies cool in the process offorming new stars.The galaxies' stars are all formed at different time periods, so the galaxies have time to cool and to build up matter to form new stars. As time passes, this star formation changes the shape of the galaxies.

Nearby examples includeNGC 1705,NGC 2915,NGC 3353andUGCA 281.[15][16][17][18]

Ultra-faint dwarf galaxies

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Ultra-faint dwarfgalaxies (UFDs) are a class ofgalaxiesthat contain from a few hundred to one hundred thousandstars,making them the faintest galaxies in theUniverse.[19]UFDs resembleglobular clusters(GCs) in appearance but have very different properties. Unlike GCs, UFDs contain a significant amount ofdark matterand are more extended. UFDs were first discovered with the advent of digital sky surveys in 2005, in particular with theSloan Digital Sky Survey(SDSS).[20][21]

UFDs are the mostdark matter-dominated systems known.Astronomersbelieve that UFDs encode valuable information about the earlyUniverse,as all UFDs discovered so far are ancient systems that have likely formed very early on, only a few million years after theBig Bangand before the epoch ofreionization.[22]Recent theoretical work has hypothesised the existence of a population of young UFDs that form at a much later time than the ancient UFDs.[23]These galaxies have not been observed in ourUniverseso far.

Ultra-compact dwarfs

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Ultra-compact dwarfgalaxies (UCD) are a class of very compact galaxies with very high stellar densities, discovered[24][25][26]in the 2000s. They are thought to be on the order of 200 light years across, containing about 100 million stars.[27]It is theorised that these are the cores of nucleated dwarf elliptical galaxies that have been stripped of gas and outlying stars bytidal interactions,travelling through the hearts of rich clusters.[28]UCDs have been found in theVirgo Cluster,Fornax Cluster,Abell 1689,and theComa Cluster,amongst others.[29] In particular, an unprecedentedly large sample of ~ 100 UCDs has been found in the core region of the Virgo cluster by the Next Generation Virgo Cluster Survey team.[30]The first ever relatively robust studies of the global properties of Virgo UCDs suggest that UCDs have distinct dynamical[31] and structural[32]properties from normal globular clusters. An extreme example of UCD isM60-UCD1,about 54 million light years away, which contains approximately 200 million solar masses within a 160 light year radius; the stars in its central region are packed 25 times more densely than stars in Earth's region in the Milky Way.[33][34] M59-UCD3is approximately the same size as M60-UCD1 with ahalf-light radius,rh,of approximately 20parsecsbut is 40% more luminous with anabsolute visual magnitudeof approximately −14.6. This makes M59-UCD3 the second densest known galaxy.[35] Based on stellar orbital velocities, two UCD in the Virgo Cluster are claimed to havesupermassive black holesweighing 13% and 18% of the galaxies' masses.[36]

Partial list

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LEDA 677373is located about 14 million light-years away.[37]
Dwarf galaxyDDO 68.[38]
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See also

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References

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  1. ^"The Milky Way Galaxy".messier.seds.org.Retrieved22 June2023.
  2. ^"The Magellanic Clouds, our galactic neighbors".earthsky.org.8 December 2021.Retrieved22 June2023.
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  4. ^ "New Recipe For Dwarf Galaxies: Start With Leftover Gas".Science Daily.19 February 2009.Retrieved29 July2015.
  5. ^ Jaggard, V. (9 September 2010)."Pictures: New Proof Spiral Galaxies Eat, Digest Dwarfs".National Geographic Society.Archived fromthe originalon 12 September 2010.Retrieved11 February2012.
  6. ^ "Hubble Sizes up a Dwarf Galaxy".ESA/Hubble.24 October 2011.Retrieved25 October2011.
  7. ^ Metz, M.; Kroupa, P. (2007)."Dwarf-spheroidal satellites: are they of tidal origin?".Monthly Notices of the Royal Astronomical Society.376(1): 387–392.arXiv:astro-ph/0701289.Bibcode:2007MNRAS.376..387M.doi:10.1111/j.1365-2966.2007.11438.x.S2CID16426005.
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  9. ^Rincon, Paul (16 August 2018)."Earliest galaxies found 'on our cosmic doorstep'".BBC News.Retrieved17 August2018.
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  11. ^ "True blue".ESA/Hubble.15 June 2015.Retrieved15 June2015.
  12. ^ Schombert, J.M.; Pildis, R.A.; Eder, J.A.; Oelmer, A. Jr. (1995)."Dwarf Spirals".The Astronomical Journal.110:2067–2074.Bibcode:1995AJ....110.2067S.doi:10.1086/117669.
  13. ^ "An intriguing young-looking dwarf galaxy".ESA/Hubble.16 March 2015.Retrieved21 March2015.
  14. ^ "WISE Discovers Baby Galaxies in the Nearby Universe".WISE.2 September 2011.Retrieved3 September2011.
  15. ^ López-Sánchez, Á. R.; Koribalski, B.; van Eymeren, J.; Esteban, C.; Popping, A.; Hibbard, J. (2010). "The environment of nearby Blue Compact Dwarf Galaxies".ASP Conference Series.421:65.arXiv:0909.5500.Bibcode:2010ASPC..421...65L.
  16. ^ Papaderos, P. (7 May 2010)."Blue Compact Dwarf Galaxies"(PDF).Centro de Astrofísica daUniversidade do Porto.
  17. ^ Noeske, K.; Papaderos, P.; Cairos, L. M. (2003)."New insights to the photometric structure of Blue Compact Dwarf Galaxies from deep Near-Infrared Studies"(PDF).Göttingen Observatory.Archived fromthe original(PDF)on 15 August 2011.
  18. ^ Meurer, G. R.; Mackie, G.; Carignan, C. (1994). "Optical observations of NGC 2915: A nearby blue compact dwarf galaxy".The Astronomical Journal.107(6): 2021–2035.Bibcode:1994AJ....107.2021M.doi:10.1086/117013.
  19. ^Simon, Joshua D. (18 August 2019)."The Faintest Dwarf Galaxies".Annual Review of Astronomy and Astrophysics.57(1): 375–415.arXiv:1901.05465.Bibcode:2019ARA&A..57..375S.doi:10.1146/annurev-astro-091918-104453.ISSN0066-4146.S2CID119384790.
  20. ^Willman, Beth; Dalcanton, Julianne J.; Martinez-Delgado, David; West, Andrew A.; Blanton, Michael R.; Hogg, David W.; Barentine, J. C.; Brewington, Howard J.; Harvanek, Michael; Kleinman, S. J.; Krzesinski, Jurek (20 June 2005)."A New Milky Way Dwarf Galaxy in Ursa Major".The Astrophysical Journal.626(2): L85–L88.arXiv:astro-ph/0503552.Bibcode:2005ApJ...626L..85W.doi:10.1086/431760.ISSN0004-637X.S2CID14851943.
  21. ^Willman, Beth; Blanton, Michael R.; West, Andrew A.; Dalcanton, Julianne J.; Hogg, David W.; Schneider, Donald P.; Wherry, Nicholas; Yanny, Brian; Brinkmann, Jon (June 2005)."A New Milky Way Companion: Unusual Globular Cluster or Extreme Dwarf Satellite?".The Astronomical Journal.129(6): 2692–2700.arXiv:astro-ph/0410416.Bibcode:2005AJ....129.2692W.doi:10.1086/430214.ISSN0004-6256.S2CID826898.
  22. ^Bovill, Mia S.; Ricotti, Massimo (10 March 2009)."Pre-Reionization Fossils, Ultra-Faint Dwarfs, and the Missing Galactic Satellite Problem".The Astrophysical Journal.693(2): 1859–1870.arXiv:0806.2340.Bibcode:2009ApJ...693.1859B.doi:10.1088/0004-637X/693/2/1859.ISSN0004-637X.S2CID14543154.
  23. ^Benitez-Llambay, Alejandro; Fumagalli, Michele (1 November 2021)."The Tail of Late-forming Dwarf Galaxies in ΛCDM".The Astrophysical Journal Letters.921(1): L9.arXiv:2110.08279.Bibcode:2021ApJ...921L...9B.doi:10.3847/2041-8213/ac3006.ISSN2041-8205.S2CID239016084.
  24. ^Hilker, M.; Infante, L.; Vieira, G.; Kissler-Patig, M.; Richtler, T. (1999). "The central region of the Fornax cluster. II. Spectroscopy and radial velocities of member and background galaxies".Astronomy and Astrophysics Supplement.134:75–86.arXiv:astro-ph/9807144.Bibcode:1999A&AS..134...75H.doi:10.1051/aas:1999434.S2CID17710039.
  25. ^Drinkwater, M. J.; Jones, J. B.; Gregg, M. D.; Phillipps, S. (2000). "Compact Stellar Systems in the Fornax Cluster: Super-massive Star Clusters or Extremely Compact Dwarf Galaxies?".Publications of the Astronomical Society of Australia.17(3): 227–233.arXiv:astro-ph/0002003.Bibcode:2000PASA...17..227D.doi:10.1071/AS00034.S2CID13161406.
  26. ^ Smith, Deborah (29 May 2003). "Star search finds millions masquerading as one".Sydney Morning Herald.p. 5.ISSN0312-6315.
  27. ^Anglo-Australian ObservatoryAstronomers discover dozens of mini-galaxiesArchived27 April 2018 at theWayback Machine0100 AEST Friday 2 April 2004.
  28. ^ Stelios Kazantzidis; Ben Moore; Lucio Mayer (2004)."Galaxies and Overmerging: What Does it Take to Destroy a Satellite Galaxy?".ASP Conference Series.327:155.arXiv:astro-ph/0307362.Bibcode:2004ASPC..327..155K.
  29. ^ Mieske; Infante; Benitez; Coe; Blakeslee; Zekser; Ford; Broadhurst; et al. (2004). "Ultra Compact Dwarf galaxies in Abell 1689: a photometric study with the ACS".The Astronomical Journal.128(4): 1529–1540.arXiv:astro-ph/0406613.Bibcode:2004AJ....128.1529M.doi:10.1086/423701.S2CID15575071.
  30. ^"The Next Generation Virgo Cluster Survey"(PDF).Retrieved20 August2023.
  31. ^Zhang, Hong-Xin; et al. (March 2015). "The Next Generation Virgo Cluster Survey. VI: The Kinematics of Ultracompact Dwarfs and Globular Clusters in M87".Astrophysical Journal.802(1): 30.arXiv:1501.03167.Bibcode:2015ApJ...802...30Z.doi:10.1088/0004-637X/802/1/30.S2CID73517961.
  32. ^ Liu, Chengze; et al. (November 2015). "The Next Generation Virgo Cluster Survey. X: Properties of Ultracompact Dwarfs in The M87, M49 and M60 Regions".Astrophysical Journal.812(1): 34.arXiv:1508.07334.Bibcode:2015ApJ...812...34L.doi:10.1088/0004-637X/812/1/34.S2CID35610312.
  33. ^ Strader, Jay; Seth, Anil C.; Forbes, Duncan A.; Fabbiano, Giuseppina; et al. (August 2013). "The Densest Galaxy".Astrophysical Journal Letters.775(1): L6.arXiv:1307.7707.Bibcode:2013ApJ...775L...6S.doi:10.1088/2041-8205/775/1/L6.S2CID52207639.
  34. ^ "Evidence for densest galaxy in nearby universe".Phys.org (Omicron Technology Ltd). 24 September 2013.Retrieved25 September2013.What makes M60-UCD1 so remarkable is that about half of this mass is found within a radius of only about 80 light years. The density of stars is about 15,000 times greater—meaning the stars are about 25 times closer to each other—than in Earth's region of theMilky Waygalaxy.
  35. ^Sandoval, Michael A.; Vo, Richard P.; Romanowsky, Aaron J.; Strader, Jay; Choi, Jieun; Jennings, Zachary G.; Conroy, Charlie; Brodie, Jean P.; Foster, Caroline; Villaume, Alexa; Norris, Mark A.; Janz, Joachim; Forbes, Duncan A. (23 July 2015). "Hiding in Plain Sight: Record-breaking Compact Stellar Systems in the Sloan Digital Sky Survey".The Astrophysical Journal.808(1): L32.arXiv:1506.08828.Bibcode:2015ApJ...808L..32S.doi:10.1088/2041-8205/808/1/L32.S2CID55254708.
  36. ^Ahn, C. P.; Seth, A. C.; den Brok, M.; Strader, J.; Baumgardt, H.; van den Bosch, R.; Chilingarian, I.; Frank, M.; Hilker, M.; McDermid, R.; Mieske, S.; Romanowsky, A. J.; Spitler, L.; Brodie, J.; Neumayer, N.; Walsh, J. L. (2017)."Detection of Supermassive Black Holes in Two Virgo Ultracompact Dwarf Galaxies".Astrophysical Journal.839(2): 72.arXiv:1703.09221.Bibcode:2017ApJ...839...72A.doi:10.3847/1538-4357/aa6972.S2CID55131811.
  37. ^"A stubborn dwarf galaxy".Retrieved6 July2016.
  38. ^"A galaxy of deception".Retrieved29 September2014.
  39. ^"Hubble's Legacy".spacetelescope.org.Retrieved2 September2019.
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