Polar-ring galaxy

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NGC 660 has a belt of gas and stars around its center that it ripped from a near neighbour during a clash about one billion years ago.[1]

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.[2] 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.[3]

The best-known polar-ring galaxies are S0s (lenticular galaxies), but from the physical point of view they are part of a wider category of galaxies, including several ellipticals.

The first four S0 galaxies that were identified as polar-ring galaxies were NGC 2685,[4] NGC 4650A,[5][6] A 0136 -0801,[3] and ESO 415 -G26.[6] While these galaxies have been extensively studied, many other polar-ring galaxies have since been identified.[7] Polar-ring S0 galaxies 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.[7]

The first polar-ring elliptical galaxies were identified in 1978. They were NGC 5128, NGC 5363, NGC 1947 and Cygnus A,[8] while the polar-ring S0 galaxies NGC 2685 and NGC 4650A were at that time indicated as resulting from similar formation processes.[8] Only some years later, when the first observations of the stellar and gas motion of polar-ring elliptical and S0 galaxies were possible with a better spectroscopic technology, the external origin of the gaseous rings was clarified.[3][6][9][10] In addition to the best-known example, NGC 5128 (Cen A), a very regular polar ring elliptical, is NGC 5266[10]

Gallery

  • NGC660 polar galaxy. 24-inch telescope on Mt. Lemmon, AZ. Courtesy Joseph D. Schulman

  • NGC 4650A, an example of a polar-ring galaxy.

References

  1. ↑ "A bizarre cosmic rarity: NGC 660". ESA/Hubble Picture of the Week. Retrieved 2 December 2013. 
  2. ↑ James Binney, Michael Merrifield (1998). Galactic Astronomy. Princeton, New Jersey: Princeton University Press. ISBN 0-691-00402-1. 
  3. ↑ 3.0 3.1 3.2 F. Schweizer, B. C. Whitmore, V. C. Rubin (1983). "Colliding and merging galaxies. II - S0 galaxies with polar rings". Astronomical Journal 88: 909–925. Bibcode:1983AJ.....88..909S. doi:10.1086/113377. 
  4. ↑ P. L. Schecter, J. E. Gunn (1978). "NGC 2685 - Spindle or pancake". Astronomical Journal 83: 1360–1362. Bibcode:1978AJ.....83.1360S. doi:10.1086/112324. 
  5. ↑ J. L. Sérsic (1967). "Southern Peculiar Galaxies III". Zeitschrift für Astrophysik 67: 306–311. Bibcode:1967ZA.....67..306S. 
  6. ↑ 6.0 6.1 6.2 B. C. Whitmore, D. B. McElroy, F. Schweizer (1987). "The shape of the dark halo in polar-ring galaxies". Astrophysical Journal 314: 439–456. Bibcode:1987ApJ...314..439W. doi:10.1086/165077. 
  7. ↑ 7.0 7.1 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. Bibcode:1990AJ....100.1489W. doi:10.1086/115614. 
  8. ↑ 8.0 8.1 Bertola, F. and Galletta, G. (1978). "A new type of galaxy with prolate structure". Astrophysical Journal 226: L115–L118. Bibcode:1978ApJ...226L.115B. doi:10.1086/182844. ,
  9. ↑ Bertola, F., Galletta, G., Zeilinger, W.~W. (1985). "Warped dust lanes in elliptical galaxies - Transient or stationary phenomena?". Astrophysical Journal 292: L51–L55. Bibcode:1985ApJ...292L..51B. doi:10.1086/184471. 
  10. ↑ 10.0 10.1 Varnas, S.R. Bertola, F., Galletta, G., Freeman, K.C., Carter, D. (1987). "NGC 5266 - an elliptical galaxy with a dust ring". Astrophysical Journal 313: 69–88,. Bibcode:1987ApJ...313...69V. doi:10.1086/164949. 

External links

See also

Morphology
Structure
Active nuclei
Energetic galaxies
Interaction
Lists
See also
  • Book:Galaxies
  • Category:Galaxies
  • Portal:Astronomy
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