Cygnus X-1
Black hole · Stellar-mass
Cygnus X-1 is a black hole pulling gas off a giant blue companion star. As the gas spirals in, it heats up to millions of degrees and glows in X-rays. It was the first object most astronomers agreed was a black hole.
- 7,200 light-years awayEven light – the fastest thing there is – needs 7,200 years to get here.
- ~21 × SunMass
- A blue supergiant starPartner
Take a closer look
How big is it?
Cygnus X-1 packs about 21 Suns’ worth of matter into a dark sphere only around 120 km across. You could drive across that distance on a motorway in about an hour. Anything that crosses that edge, the event horizon, can never come back out.
Feeding on a star’s wind
Its partner is a blue supergiant around 40 times heavier than the Sun. The two orbit closer together than Mercury is to the Sun. The giant star blows off a strong wind of gas, and the black hole gobbles some of it, forming a hot, swirling disc.
The telltale flicker
The X-rays from Cygnus X-1 flicker in less than a hundredth of a second. Something can’t flicker faster than light can cross it, so the glowing region must be tiny. That clue, plus its large mass, convinced astronomers this was a black hole.
How we found out
- 1964
Discovered by X-ray detectors on a rocket flight.
- 1971–72
Astronomers find its companion star and work out the hidden object is too heavy to be a neutron star.
- 1974
Stephen Hawking bets physicist Kip Thorne that Cygnus X-1 is NOT a black hole – hoping to lose.
- 1990
Hawking concedes the bet.
If black holes don’t let light escape, how can we see them?
We see what happens around them: gas heating up as it falls in, and stars being pulled into orbits around “nothing”.
See it yourself
Near the star Eta Cygni in the Swan’s neck. You can see the companion star with binoculars – but not the black hole!
From the encyclopedia
Read the full article on Wikipedia ↗Got it?
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