Binary stars

Two stars sometimes orbit each other due to gravitational forces. The discovery contradicted the earlier belief that close pairs of stars were merely coincidentally aligned, showing that they could in fact be gravitationally bound and move in relation to each other.
 William Herschel England 1781 Binary stars

Two stars sometimes orbit each other due to gravitational forces. The discovery contradicted the earlier belief that close pairs of stars were merely coincidentally aligned, showing that they could in fact be gravitationally bound and move in relation to each other.