Which blazar is famous as a candidate binary supermassive black hole system with roughly 12-year outbursts? The answer is OJ 287.
OJ 287 is a BL Lacertae object whose optical brightness has varied in a roughly 11- to 12-year pattern for more than a century. The recurring outbursts often show a narrow double peak, a behavior widely interpreted as evidence for a smaller supermassive black hole orbiting a much larger one.
In the leading binary model, the secondary plunges through the primary black hole’s accretion disc twice during each orbit. Those disc impacts release intense flashes, making the system a valuable laboratory for studying relativistic orbital motion, black-hole spin and gravitational-wave-driven orbital decay.
OJ 287 is properly described as a candidate or inferred binary system, not an indisputably directly imaged pair. Alternative explanations and revised models remain part of the scientific discussion. The 2022 outburst predicted by some versions of the model was not observed, placing constraints on those scenarios.