Cygnus X-1 is located about 10 000 light years from Earth. It is one of the more violent places in our Galaxy. The black hole, Cygnus X-1, contains about five times the mass of the Sun, squeezed into a tiny sphere a few kilometres in diameter. Because of its density, it possesses an enormous gravitational field, which is pulling matter away from its companion star, HDE 226868. The companion is a massive star, known as a blue supergiant. It has an extremely hot surface temperature of 31 000 K. As the gas spirals towards the black hole, it is heated even further and gives off X-rays and gamma rays. Uniquely, Integral can detect all these types of radiation.