Spiral galaxies have some parts which are very old, and some parts
which are young. The center part is called the bulge and it contains
only old stars. The spinning spiral arms have lots of gas to make new
stars.
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A Matter of Scale - interactive showing the sizes of things, from very tiny to huge - from NSF
Spiral galaxies are complex objects and have several components: a disk, a bulge, and a halo. The disk contains gas, dust, and young stars in its spiral arms. The dense bulge in the center of the disk contains mostly old stars and no gas or dust. The halo is the home of a very few, scattered stars and globular clusters. The halo is also the home of dark matter in spiral galaxies. Spirals are subdivided based on the appearance of the arms and the central region. Sa types have a large, bright central region and tightly wound arms, while Sc types have a smaller central region and loosely wound arms. Sb types are somewhere in between. Spiral galaxies can also have bar-like structures through them. These galaxies are classified as SB.
Galaxies like to live together in groups called clusters. There are
not many of spirals in a cluster usually, but they are more common
than ellipticals in the
regions between clusters.
|
A Matter of Scale - interactive showing the sizes of things, from very tiny to huge - from NSF
Spiral galaxies are complex objects and have several components: a disk, a bulge, and a halo. The disk contains gas, dust, and young stars in its spiral arms. The dense bulge or nucleus in the center of the disk contains mostly old stars and no gas or dust. The halo is the home of a very few scattered stars and globular clusters. While mostly empty of visible matter, the halo is also the realm of dark matter in spiral galaxies. Spirals are further subdivided based on the appearance of the arms and the nucleus. Sa types have large nuclei and tightly wound arms, while Sc types have small nuclei and sprawling arms. Sb types are somewhere in between. Spiral galaxies can also have bar-like structures through them. These galaxies are classified as SB, and are further subdivided a-c in the same way as regular spirals. Spiral galaxies don't come in a dwarf variety, and there are not
usually many of them in clusters compared to the number of ellipticals. But they are
more common than ellipticals in the regions between clusters. |
A Matter of Scale - interactive showing the sizes of things, from very tiny to huge - from NSF
Last modified prior to September, 2000 by the Windows Team
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