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The redshift of a distant galaxy or quasar
when it is markedly different from the redshift of another neighbouring object with which it appears to be physically linked. The redshifts observed in the spectra of galaxies and quasars are generally thought to reflect the overall expansion of the universe that has been continuing since the Big Bang. In that interpretation, the magnitude of the redshift is proportional to distance,
and distances can be inferred if redshifts are measured. If two galaxies are at the same distance, they would be expected to show the same redshift.
However, there are instances where the images of galaxies and quasars that are close together on the sky suggest the existence of a physical link or bridge between them, yet the measured redshifts of the objects are at variance. This situation could arise if the apparent connection is a coincidental alignment or if the redshift did not arise purely from the general expansion of the universe.
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