Cygnus X-1
OVERVIEW
] BLACK HOLECygnus X-1 is a stellar-mass black hole in the constellation Cygnus, 7240 from Earth. Its mass is 21.20 . It is catalogued as Cyg X-1. It was discovered in 1964.
The first widely accepted black hole, and the subject of a famous bet between Stephen Hawking and Kip Thorne. It strips gas from a blue supergiant companion, blazing in X-rays.
- WHAT IT IS
- Stellar-mass black hole
- HOW FAR
- 7240
The light arriving now left it that long ago.
THE MODEL
] LENSEDCALCULATED · NOT AN OBSERVATION · SCHWARZSCHILD RADIUS FROM THE MASS · 21.2 M☉ · ACCRETION PERSISTENT · INCLINATION 27.5° · DISC PEAK 4 030 000 K
The black disc is the shadow, 2.6 times wider than the horizon that casts it, and every ray in the frame is a null geodesic of the Schwarzschild metric. The disc starts at the innermost stable circular orbit and its colour is a temperature computed from this object's own mass; one turn of its inner edge really takes 0.0096 seconds. Drag it, or use the arrow keys, to look from another direction. The stars behind are the 498,631 this catalogue holds real distances for, drawn from where the camera actually is — but every one of them is within 170 parsecs of the Sun and this object is much further out, so what is in the frame is that whole neighbourhood seen from outside it, piled into a knot around the Sun. The rest of the sky from here is not something this catalogue knows.
IMAGES
] 1 FRAMES- NASA's Chandra X-ray Observatory; Credits: NASA/CXC
Public domain
OBSERVING
] FROM WHERE YOU AREWhat it takes to see Cygnus X-1 for yourself. Everything in this part of the page is worked out for a real horizon, a real night and the equipment you say you have.
Say where you are, and this line says when Cygnus X-1 is worth going out for.
APPARENT PLACE
] EQUINOX J2026.7Where a telescope has to be pointed today, which is not quite where the catalogue records the object: the coordinate grid itself has turned since the year 2000 the catalogue is referred to.
- RIGHT ASCENSION
- DECLINATION
- GRID TURNED SINCE
- 13.1
- PROPER MOTION SINCE
- none published
Computed for 2026-08-27 00:00 UT. No proper motion is published for Cygnus X-1, so nothing here moves the object; what separates this from the catalogued position above is the coordinate grid turning under it — about fifty arcseconds a year of precession since 2000, and the small nodding of the Earth’s axis on top of that. Aberration and refraction are not included, and neither is parallax; each is under an arcminute, which is also about as well as the catalogued position is known. The same figure for any date.
CATALOG DATA
] 3 FIELDSThe raw catalogue values, as the source published them, with the error bars where one was published — sorted by what each set of figures is about rather than by the order they happened to be stored in.
WHAT IT IS MADE OF
What the object is in itself, rather than how it happens to look from here.
- Accretion state
- persistent — a thin disc fed by a companion star
- Mass
- 21.2
WHERE IT IS AND HOW IT MOVES
Position, motion across the sky and the size it covers on it. These are measurements of the object as seen from here, so every one of them depends on where here is.
- Accretion plane inclination
- 27.5
ALSO KNOWN AS
] 2 DESIGNATIONS- Common name Cygnus X-1
- Common name Cyg X-1
LOOK IT UP ELSEWHERE
] 3 SERVICESEach link carries the identifier printed beside it. Nothing on this page is a measurement of our own, so a number that disagrees with one of these is worth reporting — and a service that has never catalogued this object under this name will say so plainly.
- SIMBADCyg X-1
Cross-identifications, measured values and the reference behind each of them.
- ADSobject:"Cyg X-1"
Papers indexed against this object rather than against the string, newest first.
- VizieR5″ around 299.5903 +35.2016
Every published table with a row at this position, searched by coordinates rather than by name.
CITE THIS PAGE
] DR1This page is live and its numbers move when an upstream refreshes, so the citation names the release the rows belong to rather than the day you read them. The release itself is frozen, republished as a bundle, and is what a data-availability statement should point at.
SpaceCatalog. Cygnus X-1 [catalogue entry]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/cyg-x1
@misc{spacecatalog_cyg-x1,
author = {{SpaceCatalog}},
title = {{Cygnus X-1}},
howpublished = {SpaceCatalog, data release DR1 (2026-08-21)},
year = {2026},
url = {https://spacecatalog.org/object/cyg-x1},
note = {Catalogue entry, data release DR1 (2026-08-21). Values from SpaceCatalog curated data.}
}The values above were taken from SpaceCatalog curated data — CC-BY-4.0. Citing this page does not replace citing that catalogue.
RECENT ACTIVITY
] 3 ITEMS- Galactic Electron-Positron Annihilation Emission from X-Ray Binaries with Transient and Persistent Jets2026-08-21 · arXiv · PAPER · Argen Gian Detoito, Henric Krawczynski
- A NuSTAR Reflection-Spectroscopy Survey of Cygnus X-12026-08-16 · arXiv · PAPER · Kshitij Duraphe, Kartik Mandar, Chooda Khanal, Gopal Bhatta
- A NuSTAR Reflection-Spectroscopy Survey of Cygnus X-12026-08-16 · arXiv · PAPER · Kshitij Duraphe, Kartik Mandar, Chooda Khanal, Gopal Bhatta
arXiv · UPDATED DAILY