SDSS J1254+0846

SDSS J1254+0846 is a face-on binary quasar pair which is in the process of merging.^[2] This binary quasar is the first resolved luminous pair to be observed in the act of merging.^[3] The pair is composed of two luminous radio-quiet quasars located at redshift z=0.44,^[3][4] being SDSS J125455.09+084653.9 (SDSS J1254+0846 A) and SDSS J125454.87+084652.1 (SDSS J1254+0846 B), or SDSS J1254+0846 collectively.^[2] These designations also refer to their host galaxies. This pair provide evidence for the theory that quasars are switched on by galactic collisions.^[2] The pair are optically separated by 3.6 arcseconds, giving the real separation as 21 kpc. Tidal tails some 75 kpc have been detected around the galaxies.^[4] Thus the two galaxies involved are disc galaxies.^[2] The pair was first detected by the Sloan Digital Sky Survey, hence the "SDSS" designations.^[5] The tidal tails were first observed by the Magellan Telescopes.^[6] A computer simulation by Thomas Cox of the Carnegie Institute corroborated the hypothesis that these were two merging galaxies.^[6] This binary quasar, was at the time of discovery in 2010, the lowest redshift binary quasar then observed.^[2]

Prior to this discovery, all quasars in merging binary pairs either involved one luminous quasar, and a second obscured or dark nucleus, or a spatially unresolved pair of active nuclei.^[2]