A galaxy contains large groups of stars, planets, gas, and dust. This matter must be held together, or the galaxy will break apart. What is responsible for holding the stars, planets, gas, and dust together in a galaxy?
Gravity is responsible for holding the stars, planets, gas, and dust together in a galaxy. The gravitational forces between all the objects in the galaxy keep them in orbit around the galaxy's center of mass, preventing them from drifting apart.
