2010ApJ...724L.166I

Recent observational results provide possible evidence that binary black holes (BBHs) exist in the center of giant galaxies and may merge to form a supermassive black hole in the process of their evolution. We first detected a periodic flux variation on a cycle of 93±1 days from the 3 mm monitor observations of a giant elliptical galaxy 3C 66B for which an orbital motion with a period of 1.05±0.03 yr had been already observed. The detected signal period being shorter than the orbital period can be explained by taking into consideration the Doppler-shifted modulation due to the orbital motion of a BBH. Assuming that the BBH has a circular orbit and that the jet axis is parallel to the binary angular momentum, our observational results demonstrate the presence of a very close BBH that has a binary orbit with an orbital period of 1.05±0.03 yr, an orbital radius of (3.9±1.0)x10^–3 pc, an orbital separation of (6.1^+1.0_–0.9)x10^–3 pc, a larger black hole mass of (1.2^+0.5_–0.2)x10⁹ M_☉, and a smaller black hole mass of (7.0^+4.7_–6.4)x10⁸ M_☉. The BBH decay time of (5.1^+60.5 _–2.5)x10² yr provides evidence for the occurrence of black hole mergers. This Letter will demonstrate the interesting possibility of black hole collisions to form a supermassive black hole in the process of evolution, one of the most spectacular natural phenomena in the universe.