Is the 5-kpc galactic arm a colony of X-ray pulsars?

MORE than two dozen binary X-ray pulsars have been discovered in our Galaxy¹. Because of instrumental constraints, however, most of these have been discovered within only a few kiloparsecs (kpc) of the Sun. Here we report the discovery by the Ginga satellite of four X-ray pulsars and three hard X-ray sources in the galactic plane at galactic latitude l~30° and a distance of about 10 kpc (the '5-kpc arm '²). This indicates that the 5-kpc arm has been the site of vigorous formation of X-ray pulsars, and that in general their distribution might be expected to be non-uniform.