The Galactic Belt of Intelligent Life

Abstract

Current estimates of the likelihood, galactic distribution and accessibility of extra-terrestrial civilizations generally contain three shortcomings: They treat our Galaxy as a homogeneous, isotropic and steady-state system and not as an object of specific geometric and kinematic properties with reasonably well understood morphology and path of evolution. If we assume that the case of mankind is about average and accept the idea that the longevity of a civilization might be limited with high probability by catastrophic events threatening during the crossing of galactic arms, intelligent life is presumably concentrated on a belt in the Galaxy which is a narrow annulus including the corotation circle and the galactic orbit of our Sun. If the galactic belt of intelligent life is a reality at least the first and last factors in the “Drake Equation” must be reevaluated. (The number of suitable stars in the belt is only of the order of 10⁸ and the average longevity of a civilisation needs to be judged in comparison with the time which its system spends between two neighbouring spiral arms.) Supposing that intelligent life will develop on the same time-scale, by the same rules wherever the proper surroundings and the needed time are given, it is possible to locate a zone of advanced civilisations where societies at least as old as ours are primarily expected. From heliocentric point of view the distribution of our potential extraterrestrial partners is highly anizotropic: in a small solid angle around the line of sight there are about 10³ times as many of them in the tangential directions than towards the galactic anticentre.