Galaxy rotation curve

A galaxy rotation curve is like a chart that shows how fast stars are spinning in a galaxy. In most galaxies, the stars at the edge spin faster than the stars in the middle. This happens because all the stars and gas in a galaxy pull on each other, like magnets, to keep things together. There is a lot of mass in the middle, where there are usually more stars, so the stars at the edges would need to spin faster to keep everything close together. The galaxy rotation curve shows how much faster the outer edges must spin to balance everything.