In a previous paper by Sillanpaa et al. we find evidence for a binary pair of supermassive black holes in OJ 287. Here we study a process in which supermassive binary black holes are formed in nuclei of supergiant galaxies due to galaxy mergers. There is growing evidence that mergers of galaxies are common and that supermassive black holes in centers of galaxies are also common. Consequently, it is expected that binary black holes should arise in connection with galaxy mergers. We first consider the merger process in a galaxy which is modeled after M87. We include Chandrasekhar's dynamical friction and the tidal break-up of the companion galaxy in calculating the orbits of the companion galaxies. After the disruption of the companion we follow the orbits of the central black holes. We derive the capture probability of a companion as a function of its mass. Assuming a correlation between the galaxy mass and the black holes mass, we calculate the expected mass ratio in binary black holes. The binary black holes formed in this process are long lived, surviving longer than the Hubble time unless they are perturbed by black holes from successive mergers. The properties of these binaries agree with Gaskell's observational work on quasars and its interpretation in terms of binary black holes.
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Valtaoja et al. (1989) studied this question.