Colour-enhanced X-ray image of Cygnus X-2 taken by the German ROSAT satellite. Cygnus X-2 is believed to be a neutron star orbiting a normal giant star of a mass similar to that of the Sun, with a period of orbit of 9.87 days. In such stellar pairings, matter from the giant star is drawn off into the immense gravitational field of the neutron star. As it approaches the neutron star, the matter is warmed and begins to emit the X-rays that help to indicate the neutron star's position. The Cygnus X-2 source is thought to be 20,000 light years from Earth. ROSAT was launched into low-Earth orbit on the Delta 195 vehicle on 1 June 1990.