  We report a correlation between the radial acceleration traced by rotation
curves and that predicted by the observed distribution of baryons. The same
relation is followed by 2693 points in 153 galaxies with very different
morphologies, masses, sizes, and gas fractions. The correlation persists even
when dark matter dominates. Consequently, the dark matter contribution is fully
specified by that of the baryons. The observed scatter is small and largely
dominated by observational uncertainties. This radial acceleration relation is
tantamount to a natural law for rotating galaxies.
