What was the first evidence that gravity outside our solar system worked the same way as it does inside?

Question

Quizplus · Accepted Answer

Herschel measured the two stars that make up the Castor system moving around each other, indicating that gravity outside our solar system works the same way as it does inside. Galileo's observations of the Milky Way, Cannon's spectral measurements, and Comet Halley's return did not provide evidence for this. The statement "we still don't know whether gravity around other stars works the same way as it does here" is incorrect, as we do have evidence to support the assumption that gravity works similarly outside our solar system.

What Was the First Evidence That Gravity Outside Our Solar