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V404 Cygni ❍｜Definition｜1st｜20260912203812-00-⌔
V404 Cygni
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.1 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.2
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.3
Printed 2026-09-12.
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Burdge, Kevin B.; El-Badry, Kareem; Kara, Erin; Canizares, Claude; Chakrabarty, Deepto; Frebel, Anna; Millholland, Sarah C.; Rappaport, Saul; Simcoe, Rob; Vanderburg, Andrew (2024-10-23). “The black hole low-mass X-ray binary V404 Cygni is part of a wide triple”. Nature. 635 (8038): 316–320. arXiv:2404.03719. Bibcode:2024Natur.635..316B. doi:10.1038/s41586-024-08120-6. ISSN 1476-4687. PMID 39443805. ↩
Kimura, Mariko; et al. (7 January 2016). “Repetitive patterns in rapid optical variations in the nearby black-hole binary V404 Cygni”. Nature. 529 (7584): 54–70. arXiv:1607.06195. Bibcode:2016Natur.529…54K. doi:10.1038/nature16452. PMID 26738590. S2CID 4463697. ↩
*Brecher, K. (1993-05-01). “Gray Holes”. American Astronomical Society Meeting Abstracts 182. 182: 55.07. Bibcode:1993AAS…182.5507B. ↩
V404 Cygni ❍｜SIMBAD｜1st｜20260912213648-00-●
V404 Cygni (Retrieved 2026-09-12.)
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