'''OJ 287''' is a [[BL Lac object]] located 3.5 [[1000000000 (number)|billion]] [[light-year]]s awayfrom 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,<ref name=SnT-2015-01-13>{{cite news |url= http://www.skyandtelescope.com/astronomy-news/black-hole-binary-en-route-merger-0113201423/ |title= Black Hole Binary En Route to Merger? |date= 13 January 2015 |author= Camille M. Carlisle |publisher= [[Sky & Telescope]] }}</ref> it was first detected at radio wavelengths during the course of the [[Ohio Sky Survey]]. It is a [[supermassive black hole]] binary.<ref name="Laine2020" /> 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.<ref name="JPL2020-04" />
