Spiral galaxies are further classified by how tightly their spiral arms are wound. A galaxy with very tightly wound arms, such the left galaxy in the list above, would be called type a. galaxy A type b galaxy has more loosely wound arms.
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The arms of a spiral galaxy have lots of gas and dust, and they are often areas where new stars are constantly forming. The bulge of a spiral galaxy is composed primarily of old, red stars. Very little star formation goes on in the bulge. The table below shows the abbreviations that are used for spiral galaxy types.
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a spiral galaxy whose center has the form of an extended bar. barred spiral galaxy. A spiral galaxy with a barlike bulge in the center, extending between the core and the spiral arms. About a third of spiral galaxies have this straight bar of stars, gas, and dust extending out from the nucleus. As with other spiral galaxies, barred spiral galaxies rotate, and new stars form from the dust and gas in their arms. Astronomers believe that some elliptical galaxies containing hints of a bar and spiral might once have been barred spiral galaxies.
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An example of a spiral galaxy, the Pinwheel Galaxy (also known as Messier 101 or NGC 5457) A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disc containing stars, gas and dust, and a central concentration of stars known as the bulge. These are surrounded by a much fainter halo of stars, many of which reside in globular clusters.
https://en.wikipedia.org/wiki/Spiral_galaxy
• SPIRAL GALAXY (noun) The noun SPIRAL GALAXY has 1 sense: 1. a galaxy having a spiral structure; arms containing younger stars spiral out from old stars at the center. Familiarity information: SPIRAL GALAXY used as a noun is very rare. Dictionary entry details.
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normal spiral galaxy. [′nȯr·məl ′spī·rəl ′gal·ik·sē] (astronomy) A galaxy that has a lens-shaped central portion with two arms that begin to coil in the same plane and in the same fashion immediately upon emerging from opposite sides of it.
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Spiral galaxies are named for the spiral structures that extend from the center into the galactic disc. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disc because of the young, hot OB stars that inhabit them.
https://en.wikipedia.org/wiki/Spiral_galaxy
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.
http://cas.sdss.org/dr6/en/proj/basic/galaxies/spirals.asp
spiral galaxy definition
Spiral galaxy is a galaxy having a spiral structure; arms containing younger stars spiral out from old stars at the center. A spiral galaxy is a galaxy having a spiral structure; arms containing younger stars spiral out from old stars at the center.