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[[Image:NGC 4650A I HST2002.jpg|right|thumb|140px|[[NGC 4650A]], an example of a polar-ring galaxy.  Credit:[[Hubble Space Telescope]]/[[NASA]]/[[ESA]].]]


A '''polar-ring galaxy''' is a type of [[galaxy]] in which an outer ring of gas and stars rotates over the poles of the galaxy.<ref name="binneymerrifield1998">{{cite book
  | author=James Binney, Michael Merrifield
  | year=1998
  | title=Galactic Astronomy
  | publisher=Princeton University Press
  | location=Princeton, New Jersey
  | id=ISBN 0-691-00402-1}}</ref>    These polar rings are thought to form when two galaxies [[interacting galaxy|gravitationally interact]] with each other.  One possibility is that a material is tidally stripped from a passing galaxy to produce the polar ring seen in the polar-ring galaxy.  The other possibility is that a smaller galaxy collides orthogonally with the plane of rotation of the larger galaxy, with the smaller galaxy effectively forming the polar ring structure.<ref name="schweizeretal1983">{{cite journal
  | author=F. Schweizer, B. C. Whitmore, V. C. Rubin
  | title=Colliding and merging galaxies. II - S0 galaxies with polar rings
  | journal=Astronomical Journal
  | year=1983
  | volume=88
  | pages=909-925
  | url=http://adsabs.harvard.edu/abs/1983AJ.....88..909S}}</ref>
The first four galaxies that were identified as polar-ring galaxies were [[NGC 2685]],<ref name="schectergunn1978">{{cite journal
  | author=P. L. Schecter, J. E. Gunn
  | title=NGC 2685 - Spindle or pancake
  | journal=Astronomical Journal
  | year=1978
  | volume=83
  | pages=1360-1362
  | url=http://adsabs.harvard.edu/abs/1978AJ.....83.1360S}}</ref> [[NGC 4650A]],<ref name="sersic1967">{{cite journal
  | author=J. L. Sérsic
  | title=Southern Peculiar Galaxies III
  | journal=Zeitschrift für Astrophysik
  | year=1967
  | volume=67
  | pages=306-311
  | url=http://adsabs.harvard.edu/abs/1967ZA.....67..306S}}</ref><ref name="whitmoreetal1987">{{cite journal
  | author=B. C. Whitmore, D. B. McElroy, F. Schweizer
  | title=The shape of the dark halo in polar-ring galaxies
  | journal=Astrophysical Journal
  | year=1987
  | volume=314
  | pages=439-456
  | url=http://adsabs.harvard.edu/abs/1987ApJ...314..439W}}</ref> [[A 0136 -0801]],<ref name="schweizeretal1983">{{cite journal
  | author=F. Schweizer, B. C. Whitmore, V. C. Rubin
  | title=Colliding and merging galaxies. II - S0 galaxies with polar rings
  | journal=Astronomical Journal
  | year=1983
  | volume=88
  | pages=909-925
  | url=http://adsabs.harvard.edu/abs/1983AJ.....88..909S}}</ref>  and [[ESO 415 -G26]].<ref name="whitmoreetal1987" />  While these galaxies have been extensively studied, many other polar-ring galaxies have since been identified.<ref name="whitmoreetal1990">{{cite journal
  | author= B. C. Whitmore, R. A. Lucas, D. B. McElroy, T. Y. Steiman-Cameron, P. D. Sackett, R. P. Olling
  | title=New observations and a photographic atlas of polar-ring galaxies
  | journal=Astronomical Journal
  | year=1990
  | volume=100
  | pages=1489-1522, 1721-1755
  | url=http://adsabs.harvard.edu/abs/1990AJ....100.1489W}}</ref>  Polar rings may be found around 0.5% of all nearby [[lenticular galaxies]], and it is possible that 5% of lenticular galaxies may have had polar rings at some point during their lifetimes.<ref name="whitmoreetal1990"/>
==References==
<div class="references-small"><references/></div>
==External links==
* [http://antwrp.gsfc.nasa.gov/apod/ap990510.html  APOD: May 10, 1999 - Polar Ring Galaxy NGC 4650A]
* [http://hubblesite.org/newscenter/archive/releases/1999/16/ Internet Voters Get Two Galaxies in One from Hubble]
* [http://space.newscientist.com/article/mg19726455.500-x-marks-the-spot-in-dark-matter-web.html?feedId=online-news_rss20 X marks the spot in dark matter web] - Polar ring galaxies offer first-hand evidence of the existence of the cosmic web, ''New Scientist'', 29 February 2008
[[Category:Galaxy morphological types]]
[[de:Polarring-Galaxie]]

Revision as of 12:09, 17 May 2008

NGC 4650A, an example of a polar-ring galaxy. Credit:Hubble Space Telescope/NASA/ESA.

A polar-ring galaxy is a type of galaxy in which an outer ring of gas and stars rotates over the poles of the galaxy.[1] These polar rings are thought to form when two galaxies gravitationally interact with each other. One possibility is that a material is tidally stripped from a passing galaxy to produce the polar ring seen in the polar-ring galaxy. The other possibility is that a smaller galaxy collides orthogonally with the plane of rotation of the larger galaxy, with the smaller galaxy effectively forming the polar ring structure.[2]

The first four galaxies that were identified as polar-ring galaxies were NGC 2685,[3] NGC 4650A,[4][5] A 0136 -0801,[2] and ESO 415 -G26.[5] While these galaxies have been extensively studied, many other polar-ring galaxies have since been identified.[6] Polar rings may be found around 0.5% of all nearby lenticular galaxies, and it is possible that 5% of lenticular galaxies may have had polar rings at some point during their lifetimes.[6]

References

  1. ↑ James Binney, Michael Merrifield (1998). Galactic Astronomy. Princeton, New Jersey: Princeton University Press. ISBN 0-691-00402-1. 
  2. ↑ 2.0 2.1 F. Schweizer, B. C. Whitmore, V. C. Rubin (1983). "Colliding and merging galaxies. II - S0 galaxies with polar rings". Astronomical Journal 88: 909-925. http://adsabs.harvard.edu/abs/1983AJ.....88..909S. 
  3. ↑ P. L. Schecter, J. E. Gunn (1978). "NGC 2685 - Spindle or pancake". Astronomical Journal 83: 1360-1362. http://adsabs.harvard.edu/abs/1978AJ.....83.1360S. 
  4. ↑ J. L. Sérsic (1967). "Southern Peculiar Galaxies III". Zeitschrift für Astrophysik 67: 306-311. http://adsabs.harvard.edu/abs/1967ZA.....67..306S. 
  5. ↑ 5.0 5.1 B. C. Whitmore, D. B. McElroy, F. Schweizer (1987). "The shape of the dark halo in polar-ring galaxies". Astrophysical Journal 314: 439-456. http://adsabs.harvard.edu/abs/1987ApJ...314..439W. 
  6. ↑ 6.0 6.1 B. C. Whitmore, R. A. Lucas, D. B. McElroy, T. Y. Steiman-Cameron, P. D. Sackett, R. P. Olling (1990). "New observations and a photographic atlas of polar-ring galaxies". Astronomical Journal 100: 1489-1522, 1721-1755. http://adsabs.harvard.edu/abs/1990AJ....100.1489W. 

de:Polarring-Galaxie

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