Large-Scale Effects of Supernova Remnants on the Galaxy: Generation and Maintenance of a Hot Network of Tunnels

It is found that a supernova rate on the order of 1 per 50 years in the gaseous disk of our Galaxy is sufficient to generate and maintain throughout the interstellar medium a mesh of interconnected tunnels containing very low-density gas. This tunnel system would have n < 10-2 , T 106 K, very low magnetic field strength, tunnel radii 10 pc, and would occupy roughly half the interstellar volume. Such a tunnel network may already have been observed in soft X-ray emission, in ultraviolet absorption of 0 vi against background stars, in the seemingly chaotic distribution of local Hi, and in the stringy appearance of velocitycorrelated large-scale H I features. Subject headings: Galaxy, The - interstellar matter - shock waves - supernova remnants - X-rays