A spiral galaxy can be described as a type of galaxy characterized by its distinctive spiral arms that radiate outward from the central bulge or nucleus. These spiral arms are composed of stars, gas, and dust, and they typically contain younger, hotter stars, giving them a bluish appearance. The bulge at the center often contains older stars and may host a supermassive black hole.
Spiral galaxies have a disk shape and are often surrounded by a faint halo of dark matter and older stars. They are categorized into various types based on their structural features, including Sa, Sb, and Sc, which reflect the tightness of the spiral arms and the size of the central bulge. Common examples of spiral galaxies include the Milky Way, the Andromeda Galaxy, and the Whirlpool Galaxy (M51).
Overall, spiral galaxies are significant in terms of star formation, galaxy evolution, and the study of cosmic structure.