Astronomy Practice Exam

What is the role of gravity in a galaxy?

1. To keep moons in orbit around planets

2. To cause stars to explode

3. To hold stars together in an island formation

4. To prevent planets from orbiting

The correct answer is: To hold stars together in an island formation

Gravity plays a crucial role in the structure and stability of galaxies, acting as the fundamental force that binds stars together within these massive systems. In a galaxy, gravity is what enables stars to cluster in an "island formation," creating the distinct structure we observe in galaxies, whether spiral, elliptical, or irregular. It keeps stars in orbit around the center of the galaxy, typically where a supermassive black hole may be present, and ensures that they are held within the galaxy’s gravitational influence. The effectiveness of gravity in creating this cohesion allows galaxies to maintain their shape and prevents stars from drifting apart into the surrounding intergalactic space. This gravitational clumping is crucial for the formation and evolution of stars and other celestial objects within the galaxy. Additionally, the distribution of mass—like dark matter—further enhances the gravitational forces at play, contributing to the overall dynamics of the galaxy.