Polar-ring galaxy
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
- ↑ James Binney, Michael Merrifield (1998). Galactic Astronomy. Princeton, New Jersey: Princeton University Press. ISBN 0-691-00402-1.
- ↑ 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.
- ↑ 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.
- ↑ J. L. Sérsic (1967). "Southern Peculiar Galaxies III". Zeitschrift für Astrophysik 67: 306-311. http://adsabs.harvard.edu/abs/1967ZA.....67..306S.
- ↑ 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.
- ↑ 6.0 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.
External links
- APOD: May 10, 1999 - Polar Ring Galaxy NGC 4650A
- Internet Voters Get Two Galaxies in One from Hubble
- 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