M33, M100 Formation and Evolution. Classification and Variants Spiral galaxies are further categorized based on the prominence of their central bulge and the tightness of their spiral arms.
Spiral Galaxies Definition: Unpacking the Density Wave Theory
In contrast, barred spirals possess a bar-shaped structure of stars running through their center, from which the spiral arms emerge. Normal spirals, designated Sa, Sb, and Sc, feature a central bulge that grows larger and a disk that becomes more rectangular as the classification moves from 'a' to 'c'.
Finally, the halo is a roughly spherical region of sparse stars and dark matter that extends far beyond the visible disk, providing the gravitational scaffolding necessary to hold the galaxy together. The primary components include the central bulge, the disk, and the halo.
Spiral Galaxies Definition: Unpacking the Density Wave Theory
Type Description Example S or SBa Tight, well-defined arms originating from a large bulge. A spiral galaxy is a classification of galaxy characterized by a flat, rotating disk containing stars, gas, and dust, along with a central concentration of stars known as the bulge.
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