Macy Huston

Dyson spheres are hypothetical megastructures built by advanced extraterrestrial civilizations to harvest radiation energy from stars. Here, we combine optical data from Gaia DR2 with mid-infrared data from AllWISE to set the strongest upper limits to date on the prevalence of partial Dyson spheres within the Milky Way, based on their expected waste-heat signatures. Conservative upper limits are presented on the fraction of stars at G ≤ 21 that may potentially host non-reflective Dyson spheres that absorb 1–90 per cent of the bolometric luminosity of their host stars and emit thermal waste-heat in the 100–1000 K range. Based on a sample of ≈2.7 × 105 stars within 100 pc, we find that a fraction less than ≈2 × 10−5 could potentially host ∼300 K Dyson spheres at 90 per cent completion. These limits become progressively weaker for less complete Dyson spheres due to increased confusion with naturally occurring sources of strong mid-infrared radiation, and also at larger distances, due to the detection limits of WISE. For the ∼2.9 × 108 stars within 5 kpc in our Milky Way sample, the corresponding upper limit on the fraction of stars that could potentially be ∼300 K Dyson spheres at 90 per cent completion is ≲8 × 10−4.