Integral discovers the galaxy’s antimatter cloud is lopsided   This is an artist’s impression of ESA’s orbiting gamma-ray observatory, Integral.   The left-hand panel shows the glow of 511 keV gamma rays coming from the annihilation of electrons by their antimatter counterparts, the positrons. The map shows the entire sky, with the galactic centre at the middle. The emission can be seen extending towards the right-hand side of the map. The right-hand panel shows the distribution of hard low mass X-ray binary stars. This stellar population has a distribution that matches the extent of the 511 keV map.   This computer model of the 511 keV gamma rays coming from the central region of the galaxy matches the asymmetry around the galactic centre. The gamma rays from the galactic centre are symmetrical and the only way to fit the observations was to assume that the asymmetry was caused by gamma rays coming from the inner disc region of the galaxy, not throughout the galaxy. This ties in with the observed distribution of hard low mass X-ray binaries. Release date: 19 June 2008