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Ask an Astrophysicist

The Question

(Submitted October 02, 1996)

I'm wondering what information you have on the X-ray source Cygnus X-1 and on it's nearby star (a blue giant).

The Answer

Cyg X-1 is believed to be a black hole binary, with a 20-35 solar mass black hole and a O9.7Iab companion. The orbital period is 5.6 days. You can learn more about black holes and X-ray binaries in Imagine the Universe! in both the Basic Level and the Advanced Level. In particular, the level 2 "Black Holes" section discusses the Cygnus X-1 binary starry system. It includes some information on the blue giant companion to the unseen compact object. The reading list at the end of the page also gives a number of good books with a great deal of information about black holes: since Cygnus X-1 is still considered to be one of the better black hole candidates, all of these books discuss the binary system in some detail.

We hope you'll take the time to browse through the sites and "read more about it".

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