Galactic rotation curve

A galactic rotation curve shows how the speed of stars orbiting a galaxy varies with their distance from the galaxy's center. According to Newtonian physics, stars farther out should orbit more slowly, but observations reveal that stars far from the center move at similar speeds to those closer in. This suggests there's more unseen mass—called dark matter—surrounding the galaxy, providing extra gravitational pull. The flat or rising rotation curves are key evidence for dark matter’s existence, helping scientists understand the galaxy's mass distribution beyond what we can see directly.