WoU-MMA: Frequency and Abundance of Binary sUpermassive bLack holes from Optical Variability Surveys (FABULOVS)

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Supermassive black holes (SMBHs) are millions to billions of times more massive than the Sun. They are commonly found at the centers of massive galaxies. When galaxies merge, their central black holes should also combine. Binary SMBHs are ideal targets for multi-messenger astronomy, but no robust detection of binary SMBH has been made, due to observational limitations. This program will systematically identify and characterize binary SMBHs. It will deliver a database of robust binary SMBH candidates and provide constraints on their abundance and evolution. It will enable reliable forecasts for gravitational wave detection. The research team will also develop dedicated outreach programs that promote diversity in science. This program will combine high-quality long-term photometric and spectroscopic synoptic surveys to systematically identify and characterize sub-pc binary SMBHs. First, it aims to identify sub-pc binary SMBHs using long-term radial velocity shifts of active galactic nucleus (AGN) broad emission lines. It will test the hypothesis that the temporal drifts represent Doppler shifts from binary orbital motion. Second, it will identify milli-pc binary SMBHs from periodically variable AGNs. It will critically distinguish periodicity from stochastic variability. Combined with follow-up observations, it will provide a database of robust sub-pc binary SMBH candidates to inform their abundance, enabling reliable forecast for gravitational wave and multi-messenger detections. The program will also be valuable for characterizing long-term AGN photometric and spectroscopic variability, advancing the general understanding of accretion disk physics, effects of accretion disk winds, and SMBH feeding and feedback. This award addresses and advances the goals of the Windows on the Universe Big Idea.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.