Astronomy Practice Exam 2025 – Complete Preparation Guide

A spiral galaxy is distinguished by its striking structure, which includes a prominent central bulge surrounded by spiraling arms. These arms are formed by concentrations of stars, gas, and dust and are typically organized into distinct, winding patterns that give the galaxy its "spiral" appearance. The bulge at the center consists mostly of older stars, while the arms are often sites of ongoing star formation, populated with young, bright stars that make the arms visually distinctive.

The overall structure of a spiral galaxy tends to have significant organization, contrasting with other galaxy types, such as elliptical galaxies, which do not have defined arms and have a more spherical shape. In the context of other options provided, the descriptions of a spherical shape without defined arms, a bright center with only a halo of hot gas, or chaotic disorganized structures do not accurately represent the orderly and notable features characteristic of spiral galaxies.