Irregular galaxy

Irregular galaxy

An irregular galaxy is a galaxy that does not fall into any of the regular classes of the Hubble sequence. 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.irregular galaxies also contain abundant amounts of gas and dust

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.

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

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.

See also

* Dwarf galaxy
* Dwarf elliptical galaxy
* Dwarf spheroidal galaxy


Wikimedia Foundation. 2010.

Игры ⚽ Поможем решить контрольную работу

Look at other dictionaries:

  • irregular galaxy — noun A galaxy which is has no spirals and is not elliptical. The Magellanic Clouds are irregular galaxies …   Wiktionary

  • irregular galaxy — Astron. a galaxy with no specific form and a relatively low mass. [1960 65] * * * …   Universalium

  • irregular galaxy — Astron. a galaxy with no specific form and a relatively low mass. [1960 65] …   Useful english dictionary

  • Pegasus Dwarf Irregular Galaxy — Observation data (J2000 epoch) Constellation Pegasus Right ascension 23h 28m 36.2s[1] …   Wikipedia

  • Sculptor Dwarf Irregular Galaxy — Infobox Galaxy name = Sculptor Dwarf Irregular epoch = J2000 type = IBmcite web title=NASA/IPAC Extragalactic Database work=Results for Sculptor Dwarf Irregular url=http://nedwww.ipac.caltech.edu/cgi bin/nph… …   Wikipedia

  • Sagittarius Dwarf Irregular Galaxy — Infobox Galaxy name = SagDIG caption = SagDIG by Hubble Space Telescope credit = NASA/ESA/STScI/AURA type = IB(s)mcite web title=NASA/IPAC Extragalactic Database work=Results for Sagittarius Dwarf Irregular url=http://nedwww.ipac.caltech.edu/cgi… …   Wikipedia

  • Barred irregular galaxy — A barred irregular galaxy is an irregular version of a barred spiral galaxy. Examples include the Large Magellanic Cloud [http://arxiv.org/pdf/astro ph/9908050] and NGC 6822. [http://edoc.ub.uni muenchen.de/archive/00000082/01/Przybilla… …   Wikipedia

  • Galaxy groups and clusters — are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation.[1] They form the densest part of the large scale structure of the universe. In models for the gravitational formation of… …   Wikipedia

  • galaxy — [n] nebula elliptical galaxy, irregular galaxy, island universe, Milky Way, spiral galaxy, star cluster, star system; concepts 370,511 …   New thesaurus

  • Galaxy — This article is about the astronomical structure. For other uses, see Galaxy (disambiguation). NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 55,000 light years in diameter and approximately 60 million light… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”