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To summarise some important details for Cygnus X-1:
The binary system is some 6000 light years distance and consists of ...
A compact mass X-ray object believed to be a black hole with event horizon radius 26km and mass about 9 solar masses. It is believed to have an associated accretion disk (fed from its supergiant companion) and two relativistic jets perpendicular to it.
A class O9.7 blue supergiant HD226868 (V1357 Cyg) of visual magnitude 8.95, which is believed to have a radius of 0.2AU (20 times our Sun) and mass 20-40 solar masses.
Although the two orbit about a centre of mass, the smaller black hole can be considered to orbit the larger blue supergiant. They are about 0.2AU apart (or 1/5 the distance of the Earth from the Sun), the period of orbit being 5.6 days!!!
Regards, Rob.
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