
The galactic rotation anomaly, whereby there is a flattening of the rotational velocity curve with radius, was the prime driver for development of the theory of ‘Dark Matter” by Jan Oort and Fred Zwicky in the 1930s, reinforced by Vera Rubin over 30 years later based on more observations of galactic rotation.
She concluded that the mass densities of galaxies were uniform well beyond the galactic bulge, requiring that some form of ‘invisible’ matter be present to account for the rotational anomaly on a purely gravitational basis.















