The radio galaxy 0402+379 is believed to host a supermassive black hole binary ( SMBHB ) .
The two compact core sources are separated by a projected distance of 7.3 pc , making it the most ( spatially ) compact resolved SMBHB known .
We present new multi-frequency VLBI observations of 0402+379 at 5 , 8 , 15 and 22 GHz , and combine with previous observations spanning 12 years .
A strong frequency dependent core shift is evident , which we use to infer magnetic fields near the jet base .
After correcting for these shifts we detect significant relative motion of the two cores at \beta = v / c = 0.0054 \pm 0.0003 at PA = -34.4 ^ { \circ } .
With some assumptions about the orbit , we use this measurement to constrain the orbital period P \approx 3 \times 10 ^ { 4 } y and SMBHB mass M \approx 15 \times 10 ^ { 9 } M _ { \odot } .
While additional observations are needed to confirm this motion and obtain a precise orbit , this is apparently the first black hole system resolved as a visual binary .