Black hole · X-ray source
Cygnus X-1
Cygnus X-1 is a strong X-ray source in the constellation Cygnus and one of the first objects recognised as a black hole. It has about 21 solar masses and lies roughly 7,200 light-years away.
The black hole orbits the blue supergiant HDE 226868 every 5.6 days and pulls gas from it. This gas heats up strongly before falling in and emits X-rays. Only the companion star is visible in binoculars.
In 1974 the physicists Stephen Hawking and Kip Thorne made a bet on whether Cygnus X-1 is a black hole. Hawking bet against it and conceded in 1990.
Key facts
- Distance
- ≈ 7,200 light-years
- Hole mass
- ≈ 21 solar masses
- Companion
- HDE 226868 (8.9 mag)
- Orbital period
- ≈ 5.6 days
More famous objects
Images: NASA, ESA, ESO, Event Horizon Telescope, Wikimedia Commons. Artist's impressions are labelled as such. Figures from published research, rounded.