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.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] 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.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
doi=10.1086/113377]

The first four galaxies that were identified as polar-ring galaxies were NGC 2685,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
doi=10.1086/112324] NGC 4650A,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] 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
doi=10.1086/165077] A 0136 -0801,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
doi=10.1086/113377] and ESO 415 -G26. While these galaxies have been extensively studied, many other polar-ring galaxies have since been identified.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
doi=10.1086/115614] 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.

References

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

ee also

* List of polar-ring galaxies