Types and morphology

Types and morphology - appearance shows little structure...

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Types and morphology Types of galaxies according to the Hubble classification scheme. An E indicates a type of elliptical galaxy; an S is a spiral; and SB is a barred-spiral galaxy. [note 1] Galaxies come in three main types: ellipticals, spirals, and irregulars. A slightly more extensive description of galaxy types based on their appearance is given by the Hubble sequence . Since the Hubble sequence is entirely based upon visual morphological type, it may miss certain important characteristics of galaxies such as star formation rate (in starburst galaxies) and activity in the core (in active galaxies ). [7] [ edit ] Ellipticals Main article: Elliptical galaxy The Hubble classification system rates elliptical galaxies on the basis of their ellipticity, ranging from E0, being nearly spherical, up to E7, which is highly elongated. These galaxies have an ellipsoidal profile, giving them an elliptical appearance regardless of the viewing angle. Their
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Unformatted text preview: appearance shows little structure and they typically have relatively little interstellar matter . Consequently these galaxies also have a low portion of open clusters and a reduced rate of new star formation. Instead they are dominated by generally older, more evolved stars that are orbiting the common center of gravity in random directions. In this sense they have some similarity to the much smaller globular clusters . [49] The largest galaxies are giant ellipticals. Many elliptical galaxies are believed to form due to the interaction of galaxies , resulting in a collision and merger. They can grow to enormous sizes (compared to spiral galaxies, for example), and giant elliptical galaxies are often found near the core of large galaxy clusters. [50] Starburst galaxies are the result of such a galactic collision that can result in the formation of an elliptical galaxy...
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This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.

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