X-ray binary. Computer artwork of an X-ray binary star system, seen from a nearby asteroid belt. Gas is being sucked from the giant blue star (centre) by the intense gravity of a super-dense object (upper right) that could be a black hole or a neutron star. The gas forms an accretion disc around the smaller star. Extreme rotation speeds within the disc generate temperatures high enough for the emission of X-rays. Such X-ray sources were discovered when telescopes were used above the Earth's atmosphere. A giant blue star is a massive, short-lived star. Neutron stars and black holes are produced when massive stars exhaust their fuel and collapse under their own gravity.