Which of the following describes a spiral galaxy?

Which of the following describes a spiral galaxy?

• A. A galaxy with a symmetrical disc and arms spiraling outward
• B. A galaxy that is elliptical in shape
• C. A galaxy with no defined shape
• D. A galaxy composed mainly of dark matter

Answer: (A)

A spiral galaxy is characterized by its distinct structure, which includes a symmetrical disc and spiral arms that extend outward from the center. These arms are composed of stars, gas, and dust, giving them a bright and intricate appearance. The center of a spiral galaxy typically contains a bulge of older stars and often has a supermassive black hole, which can influence the rotation and shape of the galaxy. The defining trait of a spiral galaxy is this arrangement of stars in a disc where the spiral arms are formed by density waves that compress the gas and dust, leading to star formation. This spiral structure is visually striking and can be easily observed in galaxies such as the Milky Way and the Andromeda Galaxy. The other options do not accurately describe a spiral galaxy. Elliptical galaxies have a more rounded, elongated shape and lack the distinctly organized structure of arms found in spiral galaxies. Galaxies with no defined shape fall under the irregular category, which does not have the symmetry associated with spiral galaxies. Additionally, while many galaxies, including spirals, may contain dark matter, this characteristic alone does not define their structure or type. Therefore, the most accurate description of a spiral galaxy is that it has a symmetrical disc with spiraling arms.

A spiral galaxy is characterized by its distinct structure, which includes a symmetrical disc and spiral arms that extend outward from the center. These arms are composed of stars, gas, and dust, giving them a bright and intricate appearance. The center of a spiral galaxy typically contains a bulge of older stars and often has a supermassive black hole, which can influence the rotation and shape of the galaxy.

The defining trait of a spiral galaxy is this arrangement of stars in a disc where the spiral arms are formed by density waves that compress the gas and dust, leading to star formation. This spiral structure is visually striking and can be easily observed in galaxies such as the Milky Way and the Andromeda Galaxy.

The other options do not accurately describe a spiral galaxy. Elliptical galaxies have a more rounded, elongated shape and lack the distinctly organized structure of arms found in spiral galaxies. Galaxies with no defined shape fall under the irregular category, which does not have the symmetry associated with spiral galaxies. Additionally, while many galaxies, including spirals, may contain dark matter, this characteristic alone does not define their structure or type. Therefore, the most accurate description of a spiral galaxy is that it has a symmetrical disc with spiraling arms.