V404 Cygni is a microquasar and a binary system in the constellation of Cygnus. It contains a black hole with a mass of about 9 M☉ and an early K giant star companion with a mass slightly smaller than the Sun. The star and the black hole orbit each other every 6.47129 days at fairly close range. Due to their proximity and the intense gravity of the black hole, the companion star loses mass to an accretion disk around the black hole and ultimately to the black hole itself.The "V" in the name indicates that it is a variable star, which repeatedly gets brighter and fainter over time. It is also considered a nova, because at least three times in the 20th century it produced a bright outburst of energy. Finally, it is a soft X-ray transient because it periodically emits short bursts of X-rays.
X-ray light echoes from the 2015 nova eruption
Observation data
Epoch J2000.0 Equinox J2000.0ConstellationCygnusRight ascension 20h 24m 03.83s
[1]Declination+33° 52′ 02.2″
[1]Apparent magnitude (V)11.2 - 18.8
[2]CharacteristicsSpectral typeK3 III
[3]U−B color index+0.3[4]B−V color index+1.5
[4]Variable typeNova
[5]AstrometryDistance2,390
[6] pcAbsolute magnitude (MV)+3.4
[7]DetailsA (black hole)Mass9
[6] M☉BMass0.7
[7] M☉Radius6.0
[7] R☉Luminosity10.2
[7] L☉Surface gravity (log g)3.50
[8] cgsTemperature4,800
[8] KRotational velocity (v sin i)36.4
[8] km/sOther designations
V404 Cyg, Nova Cygni 1938, Nova Cygni 1989, GS 2023+338, AAVSO 2020+33
Database referencesSIMBADdata
In 2009, the black hole in the V404 Cygni system became the first black hole to have an accurate parallax measurement for its distance from the Solar System. Measured by very-long-baseline interferometry using the High Sensitivity Array, the distance is 2.39±0.14 kiloparsecs,[10] or 7800±460 light-years.
In April 2019, astronomers announced that jets of particles shooting from the black hole were wobbling back and forth on the order of a few minutes, something that had never before been seen in the particle jets streaming from a black hole. Astronomers believe that the wobble is caused by the warping of space/time by the huge gravitational field in the vicinity of the black hole.
- The black hole companion has been proposed as a Q star candidate.
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