Spirals - Spirals Spiral galaxies have flattened disks with...

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Spirals Spiral galaxies have flattened disks with a spiral pattern in the disk. The spiral arms can go all of the way into the bulge or be attached to the ends of a long bar of gas and dust that bisects the bulge. The four distinguishing characteristics of the spirals are: (a) they have more orderly, rotational motion than random motion (the rotation refers to the disk as a whole and means that the star orbits are closely confined to a narrow range of angles and are fairly circular); (b) they have some or a lot of gas and dust between the stars; (c) this means they can have new star formation occuring in the disk, particularly in the spiral arms; and (d) they have a spiral structure. Spiral galaxies are sub-classified into ``a'', ``b'', ``c'', and ``d'' groups according to how loose their spiral arms are and how big the nucleus is. The ``a'' group spirals have large bulges and very tightly wound spiral arms and the ``d'' group spirals have almost no bulge and very loose arms. The Milky Way is between the ``b'' and ``c'' groups with a bar, so it is an SBbc-type spiral 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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Spirals - Spirals Spiral galaxies have flattened disks with...

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