Question

which discovery by astronomer vera rubin helped prove the existence of dark matter?
galaxies exist outside of the milky way
the expansion of the universe is accelerating
galaxies spin faster than they should, based on their visible matter
gas giants form farther from the sun, where temperatures are cooler

Explanation:

Vera Rubin observed that galaxies spin faster than expected based on the amount of visible matter they contain. This led to the idea that there is unseen mass (dark matter) providing additional gravitational pull to account for the high - speed rotation.

Answer:

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