Astrophysical existential threats: a comparative analysis

Using a simple, coarse-grained Poisson process model, we calculate – for seven types of astrophysical catastrophe – both their individual and combined threat to complex lifeforms (extraterrestrial intelligences (ETIs)) throughout the Milky Way Galaxy. In terms of cumulative effects, we calculate that ETIs are likely to be astrophysically driven extinct on timescales of roughly once every 100 million years. In terms of comparative effects, large bolide impactors represent the most significant type of astrophysical contribution to the galaxy-wide debilitation of hypothesized ETI civilizations. Nonetheless, we conclude that astrophysical existential threats – whether taken singly or in combination – are likely insufficient, alone, to explain the Fermi Paradox. Astrophysical catastrophes, while both deadly and ubiquitous, do not appear to be frequent enough to wipe out every species in the Galaxy before they can attain or utilize spacefaring status.