A theory has been developed of an auxiliary gravitational field which operates in conjunction with relativistic gravity and accounts for the empirical success of Milgrom’s modified Newtonian dynamics theory. Remarkable links between this astronomical theory and atomic physics have been discovered. Resonant, standing-wave properties of the field encourage the formation of flat rotation curves, bar or spiral structures and quantised galactic rings. Gravitational lensing due to this field is also significant. The angular momentum proportional to mass-squared relationship observed in galaxies is attributed to this field selecting a preferred galactic rotation velocity.