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Encyclopedia > Irregular galaxy
NGC1427A, an example of an irregular galaxy.
NGC1427A, an example of an irregular galaxy.

An irregular galaxy is a galaxy that does not fall into the Hubble classification for galaxies. These are galaxies that feature neither spiral nor elliptical morphology. They are often chaotic in appearance, with neither a nuclear bulge nor any trace of spiral arm structure. Collectively they are thought to make up about a quarter of all galaxies. Most irregular galaxies were once spiral or elliptical galaxies but were deformed by gravitational action. Image File history File links Download high resolution version (709x800, 68 KB) Summary Image of irregular galaxy NGC 1427A, derived from Hubble Archives. ... Image File history File links Download high resolution version (709x800, 68 KB) Summary Image of irregular galaxy NGC 1427A, derived from Hubble Archives. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 17,000 parsecs in diameter and approximately 20 million parsecs distant. ... Astronomers classify galaxies based on their overall shape (elliptical, spiral or barred spiral) and further by the specific properties of the individual galaxy (for example degree of ellipse, number of spirals or definition of bar). ... A spiral galaxy is a type of galaxy in the Hubble sequence which is characterized by the following physical properties: Spiral Galaxy M74 presents a face-on view of its spiral arms. ... An elliptical galaxy is a type of galaxy in the Hubble sequence characterized by the following physical properties: The giant elliptical galaxy NGC 4881 (the spherical glow at upper left) lies at the edge of the Coma Cluster of Galaxies. ...


There are two major Hubble types of irregular galaxies:

  • An Irr-I galaxy (Irr I) is an irregular galaxy that features some structure but not enough to place it cleanly into the Hubble sequence. de Vaucouleurs subtypes this into galaxies that have some spiral structure Sm, and those that do not Im.
  • An Irr-II galaxy (Irr II) is an irregular galaxy that does not appear to feature any structure that can place it into the Hubble sequence.

A third classification of irregular galaxies are the dwarf irregulars, labelled as dI or dIrrs. This type of galaxy is now thought to be important to understand the overall evolution of galaxies, as they tend to have a low level of metallicity and relatively high levels of gas, and are thought to be similar to the earliest galaxies that populated the Universe. They may represent a local (and therefore more recent) version of the faint blue galaxies known to exist in deep field galaxy surveys. Look up Structure in Wiktionary, the free dictionary. ... Gérard Henri de Vaucouleurs (April 25, 1918–October 7, 1995) was a French-American astronomer. ... The globular cluster M80. ... A faint blue galaxy is a distant, irregularly shaped galaxy in which star formation occurs at a high rate. ... This high resolution image of the HUDF includes galaxies of various ages, sizes, shapes, and colors. ...


Some irregular galaxies are small spiral galaxies that are being distorted by the gravity of a larger neighbour. A spiral galaxy is a type of galaxy in the Hubble sequence which is characterized by the following physical properties: Spiral Galaxy M74 presents a face-on view of its spiral arms. ...


The Magellanic Cloud galaxies were once classified as irregular galaxies, but have since been found to contain barred spiral structures, and have been since re-classified as "SBm", a fourth type of barred spiral galaxy. The two Magellanic Clouds are irregular dwarf galaxies that may be orbiting our Milky Way galaxy[1], and thus are members of our Local Group of galaxies. ... NGC 1300, viewed nearly face-on. ...


Examples

IC 1613 is an irregular galaxy and a dwarf galaxy in the Cetus constellation. ... Irregular Galaxy IC 10. ... Leo A or Leo III is an irregular galaxy in the constellation Leo. ... Messier 82 (also known as NGC 3034 or the Cigar Galaxy) is a starburst galaxy about 12 million light-years away in the constellation Ursa Major. ... NGC 1569 is an irregular galaxy and dwarf galaxy in Camelopardalis that was discovered by William Herschel on November 4, 1788. ... NGC 3109 is a small irregular galaxy between 4. ... The Pegasus Dwarf Irregular Galaxy (also known as UGC 12613, DDO 216, A2304, Peg DIG, or the Pegasus Dwarf) is an irregular galaxy and a dwarf galaxy in the Pegasus constellation. ... The Phoenix Dwarf Galaxy is a dwarf galaxy and an irregular galaxy that was discovered in 1976 by H.E. Schuster and R.M. West and mistaken for a globular cluster. ... The Sculptor Dwarf Irregular Galaxy (SDIG) —also known as ESO 349-G31 or PGC 621— is an irregular galaxy in the Sculptor group of galaxies. ... It has been suggested that this article or section be merged with Sextans Dwarf Spheroidal. ... The Wolf-Lundmark-Melotte (WLM) galaxy is an irregular galaxy discovered in 1909 by Max Wolf, and is located on the outer edges of the local group. ...

See also


  Results from FactBites:
 
Irregular galaxy - Wikipedia, the free encyclopedia (331 words)
This type of galaxy is now thought to be important to understand the overall evolution of galaxies, as they tend to have a low level of metallicity and relatively high levels of gas, and are thought to be similar to the earliest galaxies that populated the Universe.
Some irregular galaxy are small spiral galaxies that are being distorted by the gravity of a larger neighbour.
The Magellanic Cloud galaxies were once classified as irregular galaxies, but have since been found to contain barred spiral structures, and have been since re-classified as "SBm", a fourth type of barred spiral galaxy.
  More results at FactBites »

 
 

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