Which statement about spiral galaxies is true?

Which statement about spiral galaxies is true?

• A. They are generally spherical without a disk.
• B. They have a flattened disk with spiral arms.
• C. They lack rotation.
• D. They are always irregular in shape.

Answer: (B)

Spiral galaxies are defined by a rotating, flattened disk in which stars and gas orbit the center, with bright spiral arms winding through the disk. This disk structure, along with the arms, is what makes spirals distinct from rounder, featureless shapes. The arms are sites of active star formation, so they stand out with young, hot stars that light up the pattern. Because of this disk, spirals are not spherical; elliptical galaxies are more rounded and lack the organized spiral arms. They do rotate, which helps maintain the flat, disk-like appearance and the spiral pattern. Statements that describe a lack of rotation or an irregular, shape-less form don’t match what we observe in spiral galaxies.

Spiral galaxies are defined by a rotating, flattened disk in which stars and gas orbit the center, with bright spiral arms winding through the disk. This disk structure, along with the arms, is what makes spirals distinct from rounder, featureless shapes. The arms are sites of active star formation, so they stand out with young, hot stars that light up the pattern. Because of this disk, spirals are not spherical; elliptical galaxies are more rounded and lack the organized spiral arms. They do rotate, which helps maintain the flat, disk-like appearance and the spiral pattern. Statements that describe a lack of rotation or an irregular, shape-less form don’t match what we observe in spiral galaxies.