V404 Cygni
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 20h 24m 03.82s |
| Declination | +33° 52′ 02.0″ |
| Apparent magnitude (V) | 11.2 - 18.8 |
| Characteristics | |
| Spectral type | K3 III |
| U−B color index | +0.3 |
| B−V color index | +1.5 |
| Variable type | Nova |
| Astrometry | |
| Proper motion (μ) | RA: −5.177 mas/yr Dec.: −7.778 mas/yr |
| Parallax (π) | 0.3024±0.0783 mas |
| Distance | 2,390 pc |
| Absolute magnitude (MV) | +3.4 |
| Details | |
| A (black hole) | |
| Mass | 9 M☉ |
| B | |
| Mass | 0.7 M☉ |
| Radius | 6.0 R☉ |
| Luminosity | 10.2 L☉ |
| Surface gravity (log g) | 3.50 cgs |
| Temperature | 4,800 K |
| Metallicity [Fe/H] | +0.23 dex |
| Rotational velocity (v sin i) | 36.4 km/s |
| C | |
| Mass | 1.2 M☉ |
| Radius | 1.85 R☉ |
| Surface gravity (log g) | 3.95 cgs |
| Temperature | 6123 K |
| Metallicity [Fe/H] | -0.09 dex |
| Age | 4 Gyr |
| Other designations | |
| V404 Cyg, Nova Cygni 1938, Nova Cygni 1989, GS 2023+338, AAVSO 2020+33 | |
| Database references | |
| SIMBAD | data |
V404 Cygni is a microquasar and a triple star 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, and an evolved tertiary component. The inner star and the black hole orbit each other every 6.47129 days at fairly close range, while the outer tertiary takes 70000 years to orbit the inner binary system. Due to their proximity and the intense gravity of the black hole, the secondary 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.
The black hole companion has been proposed as a Q star candidate.