Discovered in the early 1960s by rocket-borne X-ray detectors, Cygnus X-1 is a binary system containing a supergiant star and a stellar-mass black hole. That black hole is both accreting matter — pulling gas off its companion and funneling it into a swirling disk — and shooting out powerful jets. The processes of accretion and jet formation give off X-rays we can detect here on Earth, but the question is, what exactly is going on?

Formerly, astronomers had developed two possible geometrical models for what the area close to the black hole looked like. Now, in a recent paper published in Nature Astronomy, researchers from Japan and Sweden have determined which model is most likely. They’ve found that this particular black hole, at least, has an extended flat accretion disk with a spherical, extended cloud of heated gas in the center.

The black hole of Cygnus X-1

Cygnus X-1 (also called Cyg X-1) is one of the most famous black holes in our galaxy. It is the first source that astronomers could agree was a black hole, and the subject of a well-known 1974 bet between Kip Thorne and Stephen Hawking. Thorne bet that Cyg X-1 was indeed a black hole, while Hawking bet that it wasn’t. By 1990, when the majority of the astronomical community had agreed the source of X-rays in Cyg X-1 was a black hole, Hawking conceded the bet (and subsequently, as per the conditions of the wager, bought Thorne a year’s subscription to Penthouse magazine.)

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