SDSS J0927+2943 (SDSS J092712.65+294344.0) is an unusual quasar. It exhibits two sets of optical emission lines with different redshifts. The origin of the two emission line systems is believed to be a gravitational wave recoil event: the ejection of a supermassive black hole from the center of the host galaxy. In this interpretation, one of the emission line systems originates in gas that is bound to the black hole, while the other set is associated with gas that remains in the galaxy. From Wikipedia
