Galaxy Rotation Curves
Why do galaxies spin faster than Newtonian gravity predicts? — Dark matter evidence
The Dark Matter Mystery
For stars far from the galactic centre, Newtonian gravity predicts v(r) ∝ 1/√r (Keplerian decline), just like planets in a solar system. But Vera Rubin (1970s) discovered that real galaxies show flat rotation curves: v(r) ≈ const at large r.
This requires an invisible mass component — the dark matter halo — with density profile described by the NFW (Navarro–Frenk–White) formula: ρ(r) = ρ₀ / [(r/rₛ)(1 + r/rₛ)²]. Dark matter makes up ~85% of total matter in the Universe yet emits no light.
Adjust sliders to see how each component contributes to the total rotation curve.