V404 Cygni
What is V404 Cygni?
Black holes & quasars· Distance 7,800 ly. A black-hole binary that woke from a 26-year sleep in June 2015, brightening hundreds of times in days while telescopes worldwide watched. Gas from the companion piles up in a disk, then crashes inward in a burst of X-rays and visible light.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where V404 Cygni is in your sky right now: https://nowsky.org/solar/sky?sel=v404 cygni — location and time set automatically, no login.
Its place in the sky
A black hole, in the direction of Cygnus.
Mass, distance, nature
| Mass | ~9 Suns |
|---|---|
| Distance | ~7,800 ly |
| Companion | K-type star lighter than the Sun, 6.5-day orbit |
| Outbursts | 1938, 1956, 1989, 2015 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Discovery and name
Famed for outbursts in 1989 and 2015, when it briefly became the brightest X-ray source and was seen by amateurs.
Frequently asked
- What is the mass of V404 Cygni?
- ~9 Suns.
- How far is V404 Cygni from Earth?
- ~7,800 ly.
- Where in the sky is V404 Cygni?
- In the direction of Cygnus.
- Where is V404 Cygni in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
Jets that change direction every few minutes
When a radio-telescope array imaged V404 Cygni's jets frame by frame during the 2015 outburst, the jets were seen changing direction on timescales of minutes to hours. The result, published in 2019, led to the interpretation that the black hole's spin axis and the accretion disk's axis are misaligned, so that the inner disk precesses rapidly through general relativity's frame-dragging and the jets wobble along with it. Until then jet precession had been known only over years.
The observation counts as a direct sighting, in a stellar black hole, of the prediction that a black hole drags the spacetime around it into rotation. V404's outbursts come once in decades, when material piled in the disk reaches a limit and collapses inward, and far better instruments than in 2015 are waiting for the next. If the 26-year cycle repeats, that will be in the early 2040s.
The black hole in depth
V404 Cygni is a black-hole binary roughly 7,800 light-years away in Cygnus. A K-type star lighter than the Sun circles a nine-solar-mass black hole every 6.5 days, and in quiet times the system is a faint eighteenth-magnitude point. Its nature emerged in 1989 when Japan's Ginga satellite caught an X-ray outburst, and old photographic plates later showed nova-like flares at the same spot in 1938 and 1956.
On 15 June 2015 the Swift satellite detected a new outburst and observatories worldwide swung toward it. For two weeks the brightness flickered violently, reaching magnitude 12 in visible light, within reach of amateur telescopes. Such outbursts are disk instabilities: gas from the companion accumulates slowly in the accretion disk until it suddenly dumps onto the black hole. This event also gave the first evidence that a black hole's jets can precess, swinging their direction like a wobbling top.
At its usual eighteenth magnitude the system is beyond amateur reach, but the next outburst should again lift it to around magnitude 12 for small telescopes. Select V404 Cygni in the Sky view to see its spot in northern Cygnus not far from Deneb, best placed on summer and autumn evenings.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.