Archive for December 4th, 2011

December 4, 2011

Cygnus X-1 mass and spin determined

Cygnus X-1 was a very puzzling object when it was discovered in 1964, because (as the name suggests) it was an extremely powerful X-ray source. Since X-rays are (fortunately) blocked by the Earth’s atmosphere, the exceptional nature of the object was only recognized when it became possible to do astronomy from above the atmosphere, in this case during a sub-orbital rocket flight. Even today, Cygnus X-1 is one of the strongest persistent X-ray sources known.

At the time of the discovery, black holes were considered to be perhaps nothing more than hypothetical objects. Their existence was allowed for as an admissible solution of the equations of general relativity, but they were considered by many astrophysicists to present such troublesome paradoxes that their actual existence was questionable. For instance, would a “naked singularity” perhaps exist inside a black hole’s event horizon? And would all the information associated with matter falling into a black hole be lost, in contradiction with principles of quantum mechanics?

In the past 50 years, overwhelming evidence has been found for the existence of both stellar-mass black holes (such as the one in Cygnus X-1) and supermassive black holes at the centers of all but the smallest galaxies. Most of the troublesome theoretical paradoxes have also been resolved. There is now abundant observational evidence that Cygnus X-1 is a binary system consisting of a black hole and a blue supergiant star (HDE 226868).

Artist’s conception – credit: Chandra X-Ray Observatory, NASA

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