Slysh haloes: the waste heat of cold computing as a submillimetre technosignature

Abstract

Searches for Dysonian waste heat have operated almost exclusively in the mid-infrared and are therefore sensitive primarily to technology radiating at 100-600K. We argue that mature, computation-dominated civilisations may instead dissipate much of their energy at far lower temperatures. The Landauer cost of irreversible computation scales linearly with temperature, while ambient temperatures at large circumstellar radii approach the 2.7K cosmic microwave background floor. Cold computation is therefore thermodynamically attractive and, because the required radiating area scales as T**-4, potentially conspicuous. These considerations predict a new object class, which we term the SLYSH HALO after the first advocate of cold Dysonian searches. A Slysh halo is a physically motivated partial Dyson swarm producing grey, line-free thermal emission from the cold outer regions of planetary systems. We show that such structures are energetically and materially plausible, and that M dwarfs provide especially favourable search targets. Archival far-infrared and submillimetre surveys of nearby stars (DEBRIS, DUNES and SONS) can in principle be reinterpreted to constrain cold circumstellar dissipation at approximately the 10**20 Watt level, several orders of magnitude below the waste-heat luminosities targeted by previous infrared searches. Additional opportunities are provided by archival observations from Planck and the JCMT, together with the reprocessing of interferometric data from facilities such as ALMA and NOEMA. We assemble six observational discriminants that separate engineered radiators from natural cold sources and outline a three-tier search programme. Even a null result would provide the first temperature-complete assessment of Dysonian technosignatures.