OJ 287
What is OJ 287?
Black holes & quasars· Distance 3.5 billion ly. Two giant black holes orbiting each other. Every 12 years the smaller one punches through the larger one's disk and the system flares, right on the schedule general relativity predicts. It lies 3.5 billion light-years away toward Cancer.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where OJ 287 is in your sky right now: https://nowsky.org/solar/sky?sel=oj 287 — location and time set automatically, no login.
Its place in the sky
A black hole, in the direction of Cancer.
Mass, distance, nature
| Mass | primary ~18 billion Suns, secondary ~150 million |
|---|---|
| Distance | ~3.5 billion ly |
| Cycle | twin flares every ~12 years |
| Records | photographic record since 1888 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Discovery and name
A blazar flaring every 12 years as a smaller black hole punches through the disk of a larger one; records go back to 1888 plates.
Frequently asked
- What is the mass of OJ 287?
- primary ~18 billion Suns, secondary ~150 million.
- How far is OJ 287 from Earth?
- ~3.5 billion ly.
- Where in the sky is OJ 287?
- In the direction of Cancer.
- Where is OJ 287 in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
The 2019 flare, predicted to within four hours
The orbital model of OJ 287 has become precise enough to predict its next flare. The one forecast for 31 July 2019 could not be seen from the ground, the source being too close to the Sun, but the Spitzer Space Telescope, trailing Earth in its orbit, could look that way and took the observation — and the flare began within four hours of the predicted time. A 12-year orbit of two black holes 3.5 billion light-years away, timed to the hour.
That precision requires all three effects of general relativity — precession of the orbit, decay of the orbit through gravitational-wave emission, and the dragging of the orbit by the large black hole's spin. OJ 287 is therefore called a natural laboratory for the strictest tests of relativity outside the solar system, and the decay of the small black hole's orbit is calculated to bring the pair to merger in about 10,000 years — the kind of event a future space-based gravitational-wave detector could catch.
The black hole in depth
OJ 287 is a blazar about 3.5 billion light-years away toward Cancer, with a brightness record stretching back to photographic plates from 1888. Combing through more than 130 years of data, astronomers found the object flaring twice every twelve years or so, and the model that explains it is a binary black hole: a secondary of about 150 million solar masses on a highly elliptical orbit around a primary of roughly 18 billion, crossing the primary's accretion disk twice per orbit.
Each plunge through the disk blasts out a bubble of hot gas, producing the flare. Because general relativity swings the orbit's closest point by 39 degrees per revolution, the flares do not follow a simple period, yet the outburst of 31 July 2019 arrived within four hours of the prediction and was confirmed by the Spitzer Space Telescope. The result is regarded as a test of the black-hole no-hair theorem.
In quiet phases it hovers around magnitude 14 to 15, a target for medium telescopes, but during flares it climbs into the twelfth-magnitude range and amateur variable-star observers track it faithfully. Select OJ 287 in the Sky view to see its position in Cancer near the Beehive Cluster, best on late-winter and spring evenings.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.