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More Information about Cygnus X-1

Chandra image of Cyg X-1
Chandra X-ray image of Cygnus X-1
(Credit: NASA/CXC/SAO)

Cygnus X-1 is one of the brightest X-ray sources seen from Earth. It was one of eight sources discovered during a sounding rocket flight in 1964. The rocket carried instruments to detect celestial sources of X-rays. The name "Cygnus X-1" tells us that the source is the brightest X-ray source within the Cygnus constellation. It us usually shortened to "Cyg X-1."

Cyg X-1 has since been found to be a binary system consisting of a blue supergiant star and a companion, which is likely a black hole. In fact, Cyg X-1 has the distinction of being the first object identified as a black hole.

The black hole's companion is a blue supergiant, called HDE226868, and is classified as an OB star. It is seen in visible wavelengths and has a radial velocity curve showing an orbital period of a little less than a week. The fact that the system is a strong X-ray emitter and that the optical and X-ray emission vary on very short time scales (as short as one one-thousandth of a second) suggest that the companion is a black hole.

The image below shows what astronomers think is going on in this system. The black hole pulls material from the blue supergiant. As the materials falls toward the black hole, it spirals in, forming a disk in the process. The X-rays are emitted by the material as it falls into the black hole.

Artist conception of Cyg X-1
Illustration showing what astronomers believe is powering Cygnus X-1. Gas from the blue supergiant is being pulled onto the companion black hole, forming a disk as it spirals in.
(Credit: NASA/CXC/M.Weiss)

Because Cyg X-1 is so bright and nearby, it is a great candidate for continuing studies of black holes. Astronomers use it to seek how black holes behave and how they affect their surroundings.

Want to know even more about Cyg X-1? Here are some resources:

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