OJ 287

OJ 287 is a BL Lac object 4 billion light-years from Earth that has produced quasi-periodic optical outbursts going back approximately 120 years, as first apparent on photographic plates from 1891. Seen on photographic plates since at least 1887, it was first detected at radio wavelengths during the course of the Ohio Sky Survey. It is a supermassive black hole binary (SMBHB). The intrinsic brightness of the flashes corresponds to over a trillion times the Sun's luminosity, greater than the entire Milky Way galaxy's light output.

Characteristics
Given the variability in the SMBHB's bursts and properties, multiple models have been proposed to account for these flashes. The initial model estimates the mass of the primary black hole to be approximately 18.35 billion solar masses and the secondary black hole around 150 million solar masses. More recent models estimate that the central supermassive black hole has a mass of 100 million solar masses, much less than previous estimations. This would make its Schwarzschild radius about 1.97 AU. The optical light curve shows that OJ 287 has a periodic variation of 11–12 years with a narrow double peak at maximum brightness. This kind of variation suggests that it is a binary supermassive black hole. The double-burst variability is thought to result from the smaller black hole punching through the accretion disc of the larger black hole twice in every 12 years.

A secondary black hole orbits the larger one with an observed orbital period of approximately 12 years and a calculated eccentricity of approximately 0.65. The maximum brightness is obtained when the minor component moves through the accretion disk of the supermassive component at perinigricon. The perinigricon and aponigricon of its orbit are about 3,250 and 17,500 AU. In recent models, the mass of the secondary supermassive black hole has been estimated to be approximately 125 million solar masses, although this has been debated through multiple studies.

An international research group, led by Stefanie Komossa, calculated the mass of the primary black hole. "The results show that an exceptionally massive black hole exceeding 10 billion solar masses is no longer needed...the results favor models with a smaller mass of 100 million solar masses for the primary black hole".

In order to reproduce all the known outbursts, the rotation of the primary black hole is calculated to be 38% of the maximum allowed rotation for a Kerr black hole.

The companion's orbit is decaying via the emission of gravitational radiation and it is expected to merge with the central black hole within approximately 10,000 years.