Cygnus X-1

[glenc]

"Cygnus X-1 is a well known galactic X-ray source (http://en.wikipedia.org/wiki/X-ray_source) in the constellation (http://en.wikipedia.org/wiki/Constellation) Cygnus (http://en.wikipedia.org/wiki/Cygnus_%28constellation%29). It was discovered in 1964 during a rocket flight (http://en.wikipedia.org/wiki/Sub-orbital_spaceflight) and is one of the strongest (http://en.wikipedia.org/wiki/Strong_%28relative_detectability%29 ) X-ray sources seen from Earth, producing a peak X-ray flux of 2.3 × 10−23 W (http://en.wikipedia.org/wiki/Watt)m (http://en.wikipedia.org/wiki/Metre)−2Hz (http://en.wikipedia.org/wiki/Hertz)−1. Cygnus X-1 was the first X-ray source widely accepted to be a black hole (http://en.wikipedia.org/wiki/Black_hole) candidate and it remains among the most studied astronomical objects (http://en.wikipedia.org/wiki/Astronomical_object) in its class. It is now estimated to have a mass about 8.7 times the mass of the Sun (http://en.wikipedia.org/wiki/Solar_mass) and has been shown to be too compact to be any known kind of normal star or other likely object besides a black hole. If so, the radius of its event horizon (http://en.wikipedia.org/wiki/Event_horizon) is probably about 26 km (http://en.wikipedia.org/wiki/Kilometer)." http://en.wikipedia.org/wiki/Cygnus_X-1
http://en.wikipedia.org/wiki/File:800px-Cygnus_X-1.jpg

The lower star in the yellow box in the attached wikisky image is next to Cyg X-1. The bright star at right is magnitude 3.9 eta Cyg and the nebula at left is Ced 173 or Sh2-101. The magnitude 8.9 star HD 226868 (next to Cyg X-1) is 26' from eta Cyg.
Sh2-101 is called the Tulip nebula. http://galaxymap.org/cgi-bin/details.py?id=22214&t=hii&s=4_p48.0xp37.0&name=S101

[seeker372011]

a 26 km event horizon!that's fascinating


would make a nice target for imaging but unfortunately for me, Northern objects are a problem :( the house gets in the way

[Robh]

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.