Astronomy
Evidence for Dark Matter from Galaxy Rotation Curves
Quick fact
Observations of galaxy rotation curves show that stars on the outskirts of galaxies orbit just as fast as those near the center, even though visible mass predicts they should slow down—implying about six times more mass than we can see.
Why this is interesting
Do you ever feel like a car's headlights only illuminate a tiny patch of road? Galaxies behave like that—but instead of darkness, we see their stars orbiting as if something unseen is pulling them.