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Irregular Galaxy

General Information

  1. Most galaxies fit one of the three types:

    Spiral The most common type of galaxy is called a "spiral galaxy." Not surprisingly, spiral galaxies look like spirals, with long arms winding toward a bright bulge at the center.
    Spiral galaxies are denoted Sa, Sb or Sc
    Elliptical Elliptical galaxies are also named because of their shapes. Elliptical galaxies range from circular (remember, a circle is an ellipse!) to long, narrow, and cigar-shaped.
    Elliptical galaxies are denoted E0-E7, near spherical to highly elongated, respectively.
    Lenticular have a central bulge, but no spiral arms. If the central bulge is not very bright, it can be very difficult to tell the difference between a lenticular galaxy and an E0 galaxy.

    Just like spiral galaxies, some lenticular galaxies have a bar. They are called "barred lenticular galaxies" and are denoted SB0. Normal lenticular galaxies are denoted S0.

    ... but about 3% of the galaxies we observe are very different: these are call Irregular

  2. These so-called "irregular galaxies" do not have a lot of common features. Many of them are the results of galaxy collisions or near misses.

  3. One type of irregular galaxy is called a "starburst galaxy." Starburst galaxies shine brightly as many new stars are born in a short period of time.

  4. Irregular galaxies are usually found in groups or clusters, where collisions and near-misses between galaxies are common. In a few irregular galaxies, astronomers can't figure out why they look so strange!
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References
Item Updated Notes
Spiral 2017-04-30 http://cas.sdss.org/dr6/en/proj/basic/galaxies/spirals.asp
Elliptical 2017-04-30 http://cas.sdss.org/dr6/en/proj/basic/galaxies/ellipticals.asp
Lenticular 2017-04-30 http://cas.sdss.org/dr6/en/proj/basic/galaxies/lenticular.asp
Irregular 2017-04-30 http://cas.sdss.org/dr6/en/proj/basic/galaxies/irregular.asp