Question

Which discovery by astronomer Vera Rubin helped prove the existence of dark matter

Answer 1

Galaxies spin faster than they should, based on their visible matter

Answer 2

When observing the Andromeda Galaxy, Vera Rubin discovered the material at the edges of the spiral-shaped galaxy (like most other galaxies) were moving at the just as fast as those at the center (almost near the black hole). This challenged the Newtonian law of motion. Therefore there had to be an unseen force that acted on these galaxies (dark matter) and space altogether.