How Fast Is Outer Milky Way Rotation?

The outer Milky Way rotates at 200 km/s — anomalously fast given the visible mass present. This anomaly was the strongest early evidence for dark matter; without it, galaxies would simply fly apart.

Galaxies rotate faster than their visible mass would allow — the strongest early evidence we had for dark matter's existence.

• Rotates faster than visible mass should allow
• Strong evidence for dark matter