gravitational redshift

A reddening of the light from a massive object caused by photons losing energy as they travel away from a region of high gravity. For the Sun, the gravitational redshift is 0.000 002; for the surface of a neutron star the theoretical value is about 1. Theorists have suggested that the large redshifts of quasars could be gravitational in origin rather than caused solely by the Doppler effect.