A Very Close Binary Black Hole in a Giant Elliptical Galaxy 3c 66b and Its Black Hole Merger

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) × 10 −3 pc, an orbital separation of (6.1 +1.0 −0.9 ) × 10 −3 pc, a larger black hole mass of (1.2 +0.5 −0.2 ) × 10 9 M ☉ , and a smaller black hole mass of (7.0 +4.7 −6.4 ) × 10 8 M ☉ . The BBH decay time of (5.1 +60.5 −2.5 ) × 10 2 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.