What holds stars, planets, gas, and dust together in a galaxy?

Gravity is the binding force that keeps together the stars, planets, gas, and dust, preserving the galaxy’s structure and ensuring the orbits of celestial objects inside it. Without gravity, galaxies would not be coherent systems.

Gravitational forces cause stars in a galaxy to orbit a common center of mass. This center is typically the galactic core, which may include a supermassive black hole. Similarly, gravitational forces influence the distribution of gas and dust as planets round their sun. During galaxy formation, gravitational forces draw gas clouds together, forcing them to collapse and generate stars. Once generated, stars inside a galaxy remain in their orbits due to gravity. The mutual gravitational attractions of stars and gas help to sustain spiral arms, disks, and bulges.