Dwarf galaxy

Source: Wikipedia, the free encyclopedia.
The Large Magellanic Cloud, a satellite galaxy of the Milky Way

A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars.[1] The Large 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

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

One theory states that most galaxies, including dwarf galaxies, form in association with

space probe identified new dwarf galaxies forming out of gases with low metallicity. These galaxies were located in the Leo Ring, a cloud of hydrogen and helium around two massive galaxies in the constellation Leo.[4]

Because of their small size, dwarf galaxies have been observed being pulled toward and ripped by neighbouring spiral galaxies, resulting in stellar streams and eventually galaxy merger.[5]

Local dwarf galaxies

The Phoenix Dwarf Galaxy is a dwarf irregular galaxy, featuring younger stars in its inner regions and older ones at its outskirts.[6]

There are many dwarf galaxies in the

Dark Ages within the first billion years after the Big Bang.[9]

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

Common types

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

Blue compact dwarf galaxies

Blue compact dwarf PGC 51017.[13]

In astronomy, a blue compact dwarf galaxy (BCD galaxy) is a small galaxy which contains large clusters of young, hot, massive stars. These stars, the brightest of which are blue, cause the galaxy itself to appear blue in colour.[14] Most BCD galaxies are also classified as dwarf irregular galaxies or as dwarf lenticular 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 of forming 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 include

UGCA 281.[15][16][17][18]

Ultra-faint dwarf galaxies

Ultra-faint dwarf galaxies (UFDs) are a class of galaxies that contain from a few hundred to one hundred thousand stars, making them the faintest galaxies in the Universe.[19] UFDs resemble globular clusters (GCs) in appearance but have very different properties. Unlike GCs, UFDs contain a significant amount of dark matter and are more extended. UFDs were first discovered with the advent of digital sky surveys in 2005, in particular with the Sloan Digital Sky Survey (SDSS).[20][21]

UFDs are the most dark matter-dominated systems known. Astronomers believe that UFDs encode valuable information about the early Universe, as all UFDs discovered so far are ancient systems that have likely formed very early on, only a few million years after the Big Bang and before the epoch of reionization.[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 our Universe so far.

Ultra-compact dwarfs

Ultra-compact dwarf galaxies (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 by tidal interactions, travelling through the hearts of rich clusters.[28] UCDs have been found in the Virgo Cluster, Fornax Cluster, Abell 1689, and the Coma 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 is M60-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]

absolute visual magnitude of approximately −14.6. This makes M59-UCD3 the densest known galaxy.[35]
Based on stellar orbital velocities, two UCD in the Virgo Cluster are claimed to have
supermassive black holes weighing 13% and 18% of the galaxies' masses.[36]

Partial list

LEDA 677373 is located about 14 million light-years away.[37]
Dwarf galaxy DDO 68.[38]

Gallery

See also

References

  1. ^ "The Milky Way Galaxy". www.messier.seds.org. Retrieved 22 June 2023.
  2. ^ "The Magellanic Clouds, our galactic neighbors". earthsky.org. 8 December 2021. Retrieved 22 June 2023.
  3. ^ "An irregular island". www.spacetelescope.org. Retrieved 25 August 2016.
  4. ^ "New Recipe For Dwarf Galaxies: Start With Leftover Gas".
    Science Daily
    . 19 February 2009. Retrieved 29 July 2015.
  5. ^ Jaggard, V. (9 September 2010). "Pictures: New Proof Spiral Galaxies Eat, Digest Dwarfs". National Geographic Society. Archived from the original on 12 September 2010. Retrieved 11 February 2012.
  6. ^ "Hubble Sizes up a Dwarf Galaxy". ESA/Hubble. 24 October 2011. Retrieved 25 October 2011.
  7. ^ Metz, M.; Kroupa, P. (2007). "Dwarf-spheroidal satellites: are they of tidal origin?".
    S2CID 16426005
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  8. ^ "New Recipe for Dwarf Galaxies: Start with Leftover Gas". Newswise.com. 18 February 2009. Retrieved 20 February 2009.
  9. ^ Rincon, Paul (16 August 2018). "Earliest galaxies found 'on our cosmic doorstep'". BBC News. Retrieved 17 August 2018.
  10. ^ Noyola, E.; Gebhardt, K.; Bergmann, M. (2008). "Gemini and Hubble Space Telescope Evidence for an Intermediate-Mass Black Hole in ω Centauri".
    S2CID 208867075
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  11. ^ "True blue". ESA/Hubble. 15 June 2015. Retrieved 15 June 2015.
  12. ^ Schombert, J.M.; Pildis, R.A.; Eder, J.A.; Oelmer, A. Jr. (1995). "Dwarf Spirals".
    doi:10.1086/117669
    .
  13. ^ "An intriguing young-looking dwarf galaxy". ESA/Hubble. 16 March 2015. Retrieved 21 March 2015.
  14. ^ "WISE Discovers Baby Galaxies in the Nearby Universe". WISE. 2 September 2011. Retrieved 3 September 2011.
  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".
    Bibcode:2010ASPC..421...65L
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  16. ^ Papaderos, P. (7 May 2010). "Blue Compact Dwarf Galaxies" (PDF). Centro de Astrofísica da
    Universidade 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 from the 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".
    doi:10.1086/117013
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  19. S2CID 119384790
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  20. S2CID 14851943
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  21. S2CID 826898
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  22. S2CID 14543154
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  23. S2CID 239016084
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  24. S2CID 17710039
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  25. S2CID 13161406
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  26. ^ Smith, Deborah (29 May 2003). "Star search finds millions masquerading as one".
    ISSN 0312-6315
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  27. ^ Anglo-Australian Observatory Astronomers discover dozens of mini-galaxies Archived 27 April 2018 at the Wayback Machine 0100 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?".
    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".
    S2CID 15575071
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  30. ^ "The Next Generation Virgo Cluster Survey" (PDF). Retrieved 20 August 2023.
  31. S2CID 73517961
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  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".
    S2CID 35610312
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  33. ^ Strader, Jay; Seth, Anil C.; Forbes, Duncan A.; Fabbiano, Giuseppina; et al. (August 2013). "The Densest Galaxy".
    S2CID 52207639
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  34. ^ "Evidence for densest galaxy in nearby universe". Phys.org (Omicron Technology Ltd). 24 September 2013. Retrieved 25 September 2013. 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 the Milky Way galaxy.
  35. S2CID 55254708
    .
  36. S2CID 55131811
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  37. ^ "A stubborn dwarf galaxy". Retrieved 6 July 2016.
  38. ^ "A galaxy of deception". Retrieved 29 September 2014.
  39. ^ "Hubble's Legacy". www.spacetelescope.org. Retrieved 2 September 2019.

External links

Wikimedia Commons has media related to Dwarf galaxies.
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