Polar-ring galaxy

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

[edit] References

  1. ^ James Binney, Michael Merrifield (1998). Galactic Astronomy. Princeton, New Jersey: Princeton University Press. ISBN 0-691-00402-1. 
  2. ^ a b F. Schweizer, B. C. Whitmore, V. C. Rubin (1983). "Colliding and merging galaxies. II - S0 galaxies with polar rings". Astronomical Journal 88: 909–925. doi:10.1086/113377. 
  3. ^ P. L. Schecter, J. E. Gunn (1978). "NGC 2685 - Spindle or pancake". Astronomical Journal 83: 1360–1362. doi:10.1086/112324. 
  4. ^ J. L. Sérsic (1967). "Southern Peculiar Galaxies III". Zeitschrift für Astrophysik 67: 306–311. 
  5. ^ a b B. C. Whitmore, D. B. McElroy, F. Schweizer (1987). "The shape of the dark halo in polar-ring galaxies". Astrophysical Journal 314: 439–456. doi:10.1086/165077. 
  6. ^ a b 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. doi:10.1086/115614. 

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