Which term describes a large system of stars, gas, and dust bound by gravity?

• A. Nebula
• B. Solar System
• C. Universe
• D. Galaxy

Answer: (D)

A galaxy is a large system of stars, gas, and dust held together by gravity. This structure spans thousands of light-years and contains billions of stars bound in one gravitational system, often with dark matter shaping its overall pull. A nebula, by contrast, is a cloud of gas and dust that may form stars but isn’t itself a bound, galaxy-sized collection of many stars. A solar system is much smaller: a single star with its surrounding planets and minor bodies. The universe includes everything—countless galaxies, all matter and energy—so it’s not a single bound system like a galaxy. So the term that best fits a large, gravity-bound collection of stars, gas, and dust is a galaxy.