Which of the following is not an observational feature associated with the binary-star system Cygnus X-1, suspected of containing a black hole?

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    X-ray emission from this region suggests the presence of a high-temperature gas.
     Rapid time variations in the X-ray radiation of Cygnus X-1 imply that the size of the X-ray emitting region is less than a few hundred kilometers across.
     Spectroscopic observation of visible light show that the binary-star system has an orbital period of less than six days.
     Its visible companion star, if on the main sequence, should have a mass about 25 times that of the Sun.
     A small, dark region in the space near the visible companion suggests light cannot escape from that region, which is the characteristic feature of a black hole.
asked Sep 20, 2012 in Astronomy by anonymous
    

1 Answer

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A small, dark region in the space near the visible companion suggests light cannot escape from that region, which is the characteristic feature of a black hole.
answered Sep 22, 2012 by SkyStar ~Expert~ (2,855 points)



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