This essay describes in depth test results and discoveries on black holesand whether or not they do exist. Special emphasis is placed on a discussion of Cygnus X-1 From the paper: "The only ways that we can detect black holes are to see the bending of light, or to examine the waves that they put off. The first thing discovered was a X-ray source in the constellation of Cygnus. This was then called Cygnus X-1 for its first X-ray source. No one knew for sure where this was coming from because X-ray telescopes cannot give that precise of a location. Later, in the spring of 1972 a new unexplained radio source was found in the same general area as Cygnus X-1. They identified this as an optical star known only by its classification number HDE226868. While we were finding this, the X-ray source for Cygnus X-1 showed up once again.
They examined the data between these two objects, and made the conclusion that they were related. Most likely as a binary pair, with the star, and the unknown object, Cygnus X-1, orbiting around each other (DeGennaro). A binary pair is a pair of stars that orbit around each other, in this case one is a black hole, and the star orbits around it. As it orbits the immense gravity from the black hole strips gas from the normal star. As it falls it is moving at such a speed that the friction causes it to heat up to several million degrees, and this heat then causes the x-rays (McClintock)."