Doppler boosting

Doppler boosting is an effect, predicted by the special theory of relativity, that enhances the radiation from material that is moving toward the observer at nearly the speed of light, and hides material moving in the opposite direction at such speeds. For example, if there are many quasars with radio jets moving at relativistic speeds, the strongest radio sources will be those that are most nearly pointed in our direction. This is important in understanding blazars and superluminal radio sources.