How did Vera Rubin provide crucial confirmation for the necessity of dark matter?

Answer

Observing constant high orbital speeds of stars at the outer edges of spiral galaxies

Vera Rubin observed that stars far from the center of spiral galaxies orbited nearly as fast as those near the center, implying an unseen mass halo providing extra gravitational anchor.

How did Vera Rubin provide crucial confirmation for the necessity of dark matter?
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