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 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,[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-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.[6]

The first polar-ring elliptical galaxies were identified in 1978. They were NGC 5128, NGC 5363, NGC 1947 and Cygnus A,[7] while the polar-ring S0 galaxies NGC 2685 and NGC 4650A were at that time indicated as resulting from similar formation processes.[7] 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.[2][5][8][9] In addition to the best-known example, NGC 5128 (Cen A), a very regular polar ring elliptical, is NGC 5266[9]

NGC 660 Polar Galaxy Gemini Observatory
NGC 660 showing Polar-Galaxy Structure

SPRC (Old Version)

The SPRC is the Sloan Polar-Ring Catalogue, an atlas of 157 polar-ring galaxies. It was put together with images from the Sloan Digital Sky Survey.There are four sections (A,B,C, and D). There are 6 galaxies in section A which are kinematically confirmed galaxies. There are 27 in section B, which are good candidates. In section C, there are 73 galaxies, which are possible candidates. And there are 51 galaxies in section D, which are related objects.

SPRC (New Version)

There is a revised version of the SPRC, with 275 candidates. There are 70 of the best candidates, 115 good candidates, 53 related objects, and 37 face-on rings.



NGC660 polar galaxy. 24-inch telescope on Mt. Lemmon, AZ.

NGC 4650A I HST2002

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

NGC 2685 HLA

NGC 2685, HST

NGC 2685 Detailed

NGC 2685, HST (A more detailed view.)

NGC 3718 HST

NGC 3718 HST

See also


  1. ^ James Binney; Michael Merrifield (1998). Galactic Astronomy. Princeton, New Jersey: Princeton University Press. ISBN 0-691-00402-1.
  2. ^ a b c 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.
  3. ^ 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.
  4. ^ J. L. Sérsic (1967). "Southern Peculiar Galaxies III". Zeitschrift für Astrophysik. 67: 306–311. Bibcode:1967ZA.....67..306S.
  5. ^ a b c 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.
  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. Bibcode:1990AJ....100.1489W. doi:10.1086/115614.
  7. ^ a b Bertola, F. & Galletta, G. (1978). "A new type of galaxy with prolate structure". Astrophysical Journal. 226: L115–L118. Bibcode:1978ApJ...226L.115B. doi:10.1086/182844.,
  8. ^ 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.
  9. ^ a b 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.CS1 maint: Multiple names: authors list (link)

External links


Centaurus is a bright constellation in the southern sky. One of the largest constellations, Centaurus was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one of the 88 modern constellations. In Greek mythology, Centaurus represents a centaur; a creature that is half human, half horse (another constellation named after a centaur is one from the zodiac: Sagittarius). Notable stars include Alpha Centauri, the nearest star system to the Solar System, its neighbour in the sky Beta Centauri, and V766 Centauri, one of the largest stars yet discovered. The constellation also contains Omega Centauri, the brightest globular cluster as visible from Earth and one of the largest known.

ESO 603-G21

ESO 603-G21 is a possible polar-ring galaxy.

II Zwicky 73

II Zwicky 73 (also known as Zw II 73) is a lenticular and polar-ring galaxy in the constellation Boötes, and about 250 million light years distant from Earth. It is an object of great scientific interest as there have been very few polar ring galaxies discovered. II Zw 73 is a very gas-rich environment. DSS and SDSS images show that it is very similar to polar ring galaxy NGC 660, the best-known of all the polar ring galaxies.

This object is also known as PGC 54461, UGC 9796, MCG+07-31-48, and PRC A-06

List of galaxies

The following is a list of notable galaxies.

There are about 51 galaxies in the Local Group (see list of nearest galaxies for a complete list), on the order of 100,000 in our Local Supercluster and an estimated number of about one to two trillion in all of the observable universe.

The discovery of the nature of galaxies as distinct from other nebulae (interstellar clouds) was made in the 1920s. The first attempts at systematic catalogues of galaxies were made in the 1960s, with the Catalogue of Galaxies and Clusters of Galaxies listing 29,418 galaxies and galaxy clusters, and with the Morphological Catalogue of Galaxies, a putatively complete list of galaxies with photographic magnitude above 15, listing 30,642. In the 1980s, the Lyons Groups of Galaxies listed 485 galaxy groups with 3,933 member galaxies. Galaxy Zoo is a project aiming at a more comprehensive list: launched in July 2007, it has classified over one million galaxy images from The Sloan Digital Sky Survey, The Hubble Space Telescope and the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey.There is no universal naming convention for galaxies, as they are mostly catalogued before it is established whether the object is or isn't a galaxy. Mostly they are identified by their celestial coordinates together with the name of the observing project (HUDF, SDSS, 3C, CFHQS, NGC/IC, etc.)

List of ring galaxies

This is a list of ring galaxies. A ring galaxy is a galaxy with a circle-like appearance. Hoag's Object, discovered by Art Hoag in 1950, is the prototypical example of a ring galaxy.

NGC 2685

NGC 2685 (also known as the Helix Galaxy) is a lenticular and polar ring Seyfert Type 2 galaxy in the constellation Ursa Major. It is about 50,000 light-years across and about 42 million light-years away from Earth. It is receding from Earth at 883 kilometers per second. It is an object of great scientific interest, because polar-ring galaxies are very rare galaxies. They are thought to form when two galaxies gravitationally interact with each other. "The bizarre configuration could be caused by the chance capture of material from another galaxy by a disk galaxy, with the captured debris strung out in a rotating ring. Still, observed properties of NGC 2685 suggest that the rotating ring structure is remarkably old and stable."Allan Sandage referred to NGC 2685 as "perhaps the most peculiar galaxy in the Shapley-Ames Catalog".

NGC 660

NGC 660 is a peculiar and unique polar-ring galaxy located approximately 45 million light years from Earth in the Pisces constellation. It is the only such galaxy having, as its host, a "late-type lenticular galaxy". It was probably formed when two galaxies collided a billion years ago. However, it may have first started as a disk galaxy that captured matter from a passing galaxy. This material could have, over time, become "strung out" to form a rotating ring.

The ring is not actually polar, but rather has an inclination from the plane of the host disk of approximately 45 degrees. The extreme number of pinkish star-forming areas that occurs along the galaxy's ring could be the result of the gravitation interaction caused by this collision. The ring is 50,000 light-years across - much broader than the disk itself - and has a greater amount of gas and star formation than the host ring. This likely indicates a very violent formation. The polar ring contains objects numbering in the hundreds. Many of these are red and blue supergiant stars. The most recently created stars in the ring were just formed approximately 7 million years ago. This indicates that the formation of these stars has been a long process and is still occurring.

Data about the dark matter halo of NGC 660 can be extracted by observing the gravitational effects of the dark matter on the disk and ring's rotation. From the core of the disk, radio waves are being emitted. The source of these waves is an area only 21 light years across. This may indicate the presence of a super-cluster of stars located within an area of cloud of gas.

The region in the centre has a vast amount of star formation, so luminous that it is considered to be a starburst galaxy.Late in 2012, this polar-ring galaxy produced an enormous outburst having a magnitude of approximately ten times brighter than a supernova explosion. The cause is not certain, but this event may have resulted from a tremendous jet being emenating from galaxy's central black hole.NGC 660 is a member of the M74 Group.

Ring galaxy

A ring galaxy is a galaxy with a circle-like appearance. Hoag's Object, discovered by Art Hoag in 1950, is an example of a ring galaxy. The ring contains many massive, relatively young blue stars, which are extremely bright. The central region contains relatively little luminous matter. Some astronomers believe that ring galaxies are formed when a smaller galaxy passes through the center of a larger galaxy. Because most of a galaxy consists of empty space, this "collision" rarely results in any actual collisions between stars. However, the gravitational disruptions caused by such an event could cause a wave of star formation to move through the larger galaxy. Other astronomers think that rings are formed around some galaxies when external accretion takes place. Star formation would then take place in the accreted material because of the shocks and compressions of the accreted material.

Active nuclei
Energetic galaxies
Low activity
See also

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