Posted by Most searches for advanced extraterrestrial civilizations assume that large-scale technology would release waste heat detectable in the mid-infrared. A new study, submitted to ‘Monthly Notices of the Royal Astronomical’, proposes that this assumption may overlook civilizations that deliberately operate their computing infrastructure at extremely low temperatures.
Astronomer Michael Garrett has introduced the concept of SLYSH haloes – hypothetical structures consisting of large numbers of artificial radiators or computing systems distributed through the cold outer regions of planetary systems. The idea is based partly on the thermodynamics of computation. According to the Landauer principle, the minimum energy required for irreversible computing decreases with temperature. Far from a star, where temperatures approach the 2.7-kelvin cosmic microwave background, advanced civilizations could therefore potentially perform computation more efficiently. Such technology would emit waste heat very differently from traditional Dyson sphere concepts. Existing searches usually target structures radiating at roughly 100-600 K in the infrared. A SLYSH halo could instead appear as faint, smooth thermal emission at far-infrared and submillimetre wavelengths.
Garrett argues that M dwarfs could be particularly promising targets because their low luminosities make very cold circumstellar environments easier to achieve. Importantly, astronomers may not need new telescopes to begin searching. Archival observations from surveys and facilities including ALMA, NOEMA, Planck, JCMT, DEBRIS, DUNES, and SONS could potentially be reanalyzed for these signals.
The paper does not report evidence of extraterrestrial technology. Instead, it identifies a previously underexplored region of SETI parameter space and proposes observational criteria for distinguishing artificial cold radiators from natural sources such as debris disks. If confirmed as a useful search strategy, SLYSH haloes could broaden SETI beyond traditional radio signals and warm Dyson-like structures. The concept highlights how assumptions about energy use and computation may shape which technological civilizations current surveys are capable of detecting.
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