The blazar OJ 287 is known for its quasi-periodic flares with periods of about 12 and 55 years, explained by a binary black hole model: a secondary black hole of about 1.5 × $10^8$ solar masses orbits a primary of 1.8 × $10^{10}$ solar masses on a precessing elliptical orbit. Flares occur when the secondary crosses the primary's accretion disk. The model has successfully predicted flares since 1982, but the October 2022 flare was the first opportunity to test the prediction of a tidal flare associated with an impact at the orbit's apocenter. A debate arose over the flare's interpretation: some considered it an impact flare, others a tidal one. This work resolves the debate using data from a multiwavelength campaign, showing that the flare was indeed tidal, as the model predicted. This matters because tidal flares allow independent determination of orbital parameters and the primary mass, as well as tests of precession theory.
The observing campaign covered a broad spectral range: optical photometry and polarimetry with telescopes worldwide (including Krakow and Jena observatories, the Nordic Optical Telescope, and ATLAS), plus ultraviolet and X-ray data from the Swift satellite. R-band light curves were constructed with one-day sampling and compared with model calculations of tidal flares from Pihajoki et al. (2013). The model accounts for particle ejection from the disk upon impact, their motion toward the jet at about 0.22 times the speed of light, and subsequent synchrotron emission. To test the flare's nature, the spectral index, polarization degree, and flux ratios across bands (V/X, V/U, V/W2) were analyzed. Additionally, the primary mass was estimated from the correlation between black hole mass and the width of the hydrogen Hβ line, accounting for the disk's inclination to the line of sight.
The October 2022 flare exhibited all signatures of a tidal flare: a double peak (the second peak in 2023 arrived a month earlier than predicted, but within statistical fluctuations), a polarization degree of about 25% (higher than the typical 10%), a flat spectral index of about -1.2, and a threefold increase in the V/X ratio relative to the background level. The observed peak flux of 2.4 mJy agrees well with the model value of 1.8 mJy after correction for disk density. Comparison with similar flares in 2005 and 2016 confirmed that all arise from successive passages of the secondary through the orbit's apocenter. The primary black hole mass derived from orbital precession is (18.35 ± 0.05) × $10^9$ solar masses, while the independent estimate from the Hβ correlation gives (1.9 ± 0.5) × $10^{10}$ solar masses, consistent within errors. This closes objections based on the assumption of an impact flare nature.
This work strengthens the binary black hole model in OJ 287 as the most precise tool for measuring supermassive black hole masses dynamically. Unlike neighboring studies that often focus on individual flares or indirect mass estimates, here a detailed comparison of a predicted tidal flare with multiwavelength observations is performed for the first time, showing that tidal flares can serve as independent confirmation of the orbital solution. It also demonstrates that tidal flares, though less precise in timing than impact flares, are still useful for testing the model on historical data where impact flares were not observed. Furthermore, the work highlights the importance of accounting for disk inclination when using empirical correlations to estimate black hole masses in blazars.
The topic could develop toward more accurate modeling of tidal flares, incorporating realistic density distributions in the disk and variable flow speeds toward the jet. Future observations of the next apocenter passages (roughly 60 years from now) will allow testing the reproducibility of predictions. Searching archival data for flares in 1896–1913 and 1945–1964 could provide additional points to refine the orbit and mass. Advances in polarization and spectral index analysis will help better distinguish tidal flares from other types of variability in blazars.
The results will influence research on binary supermassive black holes, methods for measuring their masses, and understanding of accretion disk and jet physics in active galactic nuclei.
Next steps include searching and analyzing archival photographic plates to identify tidal flares in past cycles, as well as preparing for observations of future passages of the secondary through the disk.
This work directly addresses the unresolved problem of precisely measuring supermassive black hole masses in active galactic nuclei, where spectroscopic methods often yield large uncertainties due to weak emission lines and unknown disk inclination. It also touches on distinguishing jet contribution from thermal disk emission in blazars, and the challenge of predicting flare times in systems with precessing orbits.
OJ 287 has been observed since 1888, and its 137-year-long light curve contains flares predicted by the model decades in advance. The seven brightest flares in history include four impact flares and three tidal flares, with some historical flares visible only as tidal due to gaps in observations.
The idea of a binary supermassive black hole periodically flaring as it crosses an accretion disk echoes the image of a 'black hole lighthouse' from science fiction, such as in Greg Egan's novel 'The Clockwork Rocket', where orbiting bodies around black holes produce predictable emissions.