Expanding shell structures in the galactic interstellar medium discovered by H I line observations

Measurements of the 21 cm line of neutral hydrogen have led to the discovery of expanding shell structures in the intergalactic medium. The Effelsberg 100 m telescope has been used to study one of these shells, located at galactic longitude 130 deg and latitude 22.5 deg. The velocity of expansion of this shell is about 12.5 km/s, the velocity of its center of mass is about -5.5 km/s, its diameter is about 24.5 pc, its distance is about 460 pc, and the shell gas temperature has a relatively cold temperature below 500 K. The relationship of the shell with an original supernova explosion and with nearby pulsars is theoretically discussed. The existence of cold hydrogen structures above the galactic plane which are falling toward the plane is emphasized.