A search for recoiling supermassive black hole candidates recently yielded the best candidate thus far , SDSS J092712.65+294344.0 reported by Komossa et al .
Here we propose the alternative hypothesis that this object is a supermassive black hole binary .
From the velocity shift imprinted in the emission-line spectrum we infer an orbital period of \sim 190 years for a binary mass ratio of 0.1 , a secondary black hole mass of 10 ^ { 8 } ~ { } { M } _ { \odot } , and assuming inclination and orbital phase angles of 45 ^ { \circ } .
In this model the origin of the blueshifted narrow emission lines is naturally explained in the context of an accretion flow within the inner rim of the circumbinary disk .
We attribute the blueshifted broad emission lines to gas associated with a disk around the accreting secondary black hole .
We show that , within the uncertainties , this binary system can be long lived and thus , is not observed in a special moment in time .
The orbital motion of the binary can potentially be observed with the VLBA if at least the secondary black hole is a radio emitter .
In addition , for the parameters quoted above , the orbital motion will result in a \sim 100 ~ { } { km s ^ { -1 } } velocity shift of the emission lines on a time scale of about a year , providing a direct observational test for the binary hypothesis .