One of the most important 'quantities' an astronomer can know about a celestial object is the amount of energy it emits at different wavelengths. Wavelengths are like colours and, just as the different wavelengths of optical light are distinguished as colours by our eyes and brains, Integral will use the Spectrometer on Integral (SPI) to split the gamma rays it captures into gamma-ray 'colours'. Here, SPI has captured gamma rays from the black hole, Cygnus X-1 and from the neutron star system, Cygnus X-3 in an observation that took place during 21-22 November 2002. The gamma rays do not come from the black hole but are emitted by a swirling disc of ultra-hot gas that surrounds the black hole. This is created as the black hole's gravitational field pulls matter from its companion star, HDE 226868. SPI's unique capabilities will investigate whether a cloud of antimatter envelops Cygnus X-1, as some astronomers believe.
Cygnus X-1 is about 10 000 light years from Earth and one of the brightest high-energy emitters in the sky. It was discovered in the 1960s and is thought to be a black hole, ripping its companion star to pieces. The companion star, HDE 226868, is a blue supergiant with a surface temperature of around 31 000K. It orbits the black hole once every 5.6 days.