Irregular galaxy

From Wikipedia, the free encyclopedia

This article or section does not adequately cite its references or sources.
Please help improve this article by adding citations to reliable sources. (help, get involved!)
This article has been tagged since December 2006.
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.

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 irregular galaxies 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.


This galaxy-related article is a stub. You can help Wikipedia by expanding it.
Retrieved from "http://en.wikipedia.org../../../i/r/r/Irregular_galaxy.html"
Advanced Search
Included Web Search Engines


Safe Search

close

Top Matching Results

Occasionally Search.com will highlight specialized results that are based on the context of your query. Examples of specialized results include specific links to news, images, or video.

Top Matching Results may highlight information from other Search.com pages, content from the CNET Network of sites, or third party content. The listings are based purely on relevance. Search.com does not receive payment for listings in this section but our partners that provide this data may get paid for listing these products.

Sponsored Links

This section contains paid listings which have been purchased by companies that want to have their sites appear for specific search terms and related content. These listings are administered, sorted and maintained by a third party and are not endorsed by Search.com.

Search Results

Search.com sends your search query to several search engines at one time and integrates the results into one list which has been sorted by relevance using Search.com's proprietary algorithm. You can customize the list of search engines included in your metasearch from the preferences.

The search engines that are used in your metasearch may allow companies to pay to have their Web sites included within the results. To view the Paid Inclusion policy for a specific search engine, please visit their Web site. Search.com does not accept payment or share revenue with any search engine partner for listings in this section.