A test of the massive binary black hole hypothesis: Arp 102B

The emissionline spectra of several active galactic nuclei (AGNs) have broad peaks which are significantly displaced in velocity with respect to the host galaxy. An interpretation of this effect in terms of orbital motion of a binary black hole predicts periods of a few centuries^1,2. Here we point out that recent measurements of the masses and sizes of many lowluminosity AGNs imply orbital periods much shorter than this. In particular, we find that the elliptical galaxy Arp 102B is the most likely candidate for observation of radial velocity variations; its period is expected to be ~ 3 yr. We have monitored the Ha line profile of Arp 102B for 5 yr without detecting any change in velocity, and thus find that a rather restrictive observational test of the massive binary black hole hypothesis already exists, albeit for this one object.