Dwarf galaxy

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Image of the Phoenix Dwarf Galaxy


A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars. The Large Magellanic Cloud, containing over 30 billion stars, is sometimes classified as a dwarf galaxy while others consider it a full-fledged galaxy going around the Milky Way galaxy.

[edit] Creation of dwarf galaxies

Current theory believes most galaxies, including dwarf galaxies, form in association with dark matter or out of gas containing metals. However, NASA's Galaxy Evolution Explorer space probe identified new dwarf galaxies forming out of gases lacking metals. These galaxies were located in the Leo Ring, a cloud of hydrogen and helium around two massive galaxies in the constellation Leo.[1]

[edit] Local dwarfs

There are many dwarf galaxies in the Local Group: these small galaxies frequently orbit around larger galaxies, such as the Milky Way, the Andromeda Galaxy and the Triangulum Galaxy. A recent paper [2] has suggested that many dwarf galaxies were created by tidal forces during the early evolution of the Milky Way and Andromeda. Tidal dwarf galaxies are produced when galaxies collide and their gravitational masses interact. Streams of galactic material are pulled out away from the parent galaxies and the halos of dark matter that surround them.[3]

The Milky Way has 14 known dwarf galaxies orbiting it, and recent discoveries[citation needed] have also led astronomers to believe the largest globular cluster in the Milky Way, Omega Centauri, is in fact the core of a dwarf galaxy with a black hole in its center,[4] which was at some time absorbed by the Milky Way. (See Milky Way for more information.)

[edit] Dwarf galaxies

Dwarf galaxies come in many different morphologies:

[edit] Hobbit galaxies

The recently coined term, hobbit galaxy has been used to describe galaxies smaller and dimmer than dwarf galaxies.[5][6]

[edit] Ultra Compact Dwarfs

Ultra Compact Dwarf galaxies (UCD) are a recently discovered class of very compact galaxies with very high stellar population counts. They are thought to be on the order of 200 light years across, with a hundred million stars. [7] It is theorized that these are the cores of nucleated dwarf elliptical galaxies, that have been stripped of gas and outlying stars by tidal interactions, travelling through the hearts of rich clusters. [8] UCDs have been found in the Virgo Cluster, Fornax Cluster, Abell 1689, Coma Cluster, amongst other clusters. [9]

[edit] Partial list of dwarf galaxies

[edit] References

  1. ^ UPI, "New Recipe For Dwarf Galaxies: Start With Leftover Gas", Science Daily, 19 Feb 2009[1]
  2. ^ Metz, M (2007) Dwarf-spheroidal satellites: are they of tidal origin? http://arxiv.org/abs/astro-ph/0701289
  3. ^ New Recipe for Dwarf Galaxies: Start with Leftover Gas Newswise, Retrieved on February 20, 2009.
  4. ^ UPI, Black hole found in Omega Centauri ,April 10, 2008 at 2:07 PM
  5. ^ SPACE.com - New 'Hobbit' Galaxies Discovered Around Milky Way
  6. ^ http://sciencenow.sciencemag.org/cgi/content/full/2007/109/1
  7. ^ Anglo-Australian Observatory Astronomers discover dozens of mini-galaxies 0100 AEST Friday 2 April 2004
  8. ^ arXiv, Galaxies and Overmerging: What Does it Take to Destroy a Satellite Galaxy? Mon, 21 Jul 2003 10:33:02 GMT
  9. ^ arXiv, Ultra Compact Dwarf galaxies in Abell 1689: a photometric study with the ACS, Mon, 28 Jun 2004 08:34:37 GMT

[edit] See also

[edit] External links

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