Irregular galaxy

NGC 1427A, an example of an irregular galaxy. It is an Irr-I category galaxy about 52 Mly distant.

An irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy.[1] The shape of an irregular galaxy is uncommon they do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance, with neither a nuclear bulge nor any trace of spiral arm structure.[2]

Collectively they are thought to make up about a quarter of all galaxies. Some irregular galaxies were once spiral or elliptical galaxies but were deformed by disorders in gravitational pull. Irregular galaxies may contain abundant[3] amounts of gas and dust. This is not necessarily true for Dwarf Irregulars.[4]

Types

There are three major types of irregular galaxies:[5]

Some of the irregular galaxies, especially of the Magellanic type, are small spiral galaxies that are being distorted by the gravity of a larger neighbor.

Magellanic Clouds

The Magellanic Cloud galaxies were once classified as irregular galaxies. The Large Magellanic Cloud has since been re-classified as type SBm [7] a type of barred spiral galaxy, the barred Magellanic spiral type. The Small Magellanic Cloud remains classified as an irregular galaxy of type Im under current Galaxy morphological classification, although it does contain a bar structure. Therefore, newer classification schemes place the SMC outside the irregular class as well.

Gallery

  1. ^ "A distinctly disorganised dwarf". Retrieved 29 March 2016. 
  2. ^ "Meeting the neighbours". www.spacetelescope.org. ESA/Hubble. Retrieved 8 June 2015. 
  3. ^ "A spattering of blue". www.spacetelescope.org. ESA/Hubble. Retrieved 8 September 2014. 
  4. ^ "A cosmic optical illusion". ESA/Hubble Picture of the Week. Retrieved 20 August 2013. 

See also

References

  1. Butz, Stephen D. (2002). Science of Earth Systems. Cengage Learning. p. 107. ISBN 978-0-7668-3391-3.
  2. Morgan, W. W. & Mayall, N. U. (1957). "A Spectral Classification of Galaxies." Publications of the Astronomical Society of the Pacific. 69 (409): 291303.
  3. Faulkes Telescope Educational Guide - Galaxies - Irregulars
  4. Walter, F. et al. Astophys J 661, 102 - 114, 2007
  5. Gallagher, J. S. & Hunter, D. A. (1984). "Structure and Evolution of Irregular Galaxies." Annual Review of Astronomy and Astrophysics. 22: 37-74. doi:10.1146/annurev.aa.22.090184.000345
  6. Grebel, Eva K. (2004). The evolutionary history of Local Group irregular galaxies. in McWilliam, Andrew; Rauch, Michael (eds) Origin and evolution of the elements. Cambridge University Press. p. 234-254. ISBN 978-0-521-75578-8.
  7. Corso, G. and Buscombe, W. The Observatory, 90, 229 - 233 (1970) On the spiral structure of the Large Magellanic Cloud

External links

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