Dyson Sphere Search HistoryA number of searches for Dyson Spheres have been made in the past. A few candidates have been identified but discounted for various reasons.
Sagan and Walker carried out an early analysis of the possibility of detecting a Dyson Sphere. They showed that a search out to 1000 pc was feasible even with sixties technology but that the possible confusion with natural signatures could require searches for other artifacts of intelligence such as radio signals associated with a candidate source.
Jugaku and colleagues have carried out a series of searches for partial Dyson Spheres. Typically they use the 2.2 μm K band as an indicator of the photospheric radiation of a star hosting a partial Dyson Sphere and then look for an infrared excess in the IRAS infrared satellite 12 μm band. A 1 magnitude difference would arise if the Dyson Sphere covered 1% of the host star. The measured differences are characteristically less than 0.3 magnitude which is consistent with measurement errors. They selected a set of 1774 stars from the Woolley catalog nearer than 25 pc and found 458 with matches in the 12 μm IRAS band. They have looked at 384 of these stars for infrared excesses. With the exception of a few cases discussed in their 1990 article they have found no sources with excesses suggestive of a partial Dyson Sphere covering as much as 1% of the host star.
Slysh and Timofeev at al. have used the IRAS database for a different approach. Slysh investigates the flux at the maximum of a Dyson Sphere spectrum. He estimates that all Dyson Spheres with temperatures from 50 to 400 ºK within 1 kpc of the sun should have been detected. The Timoreev search looked at a population of IRAS sources in the 110-120 and 280-290 ºK temperature range as established by Kardashev and others and did Planck blackbody fits to the four IRAS bands. They fitted by minimizing to a Planck distribution. (Note that no Planck spectrum correction is made on the four measured fluxes from the filters.) Sylsh identified one possible Dyson Sphere candidate, G357.3-1.3. The Timofeev at al. search identified 10 or so candidates but ruled out most of them, often on the basis of associations.
More recently several other searches have been conducted for partial Dyson Spheres. Globus, Backman, and Witteborn have searched by looking for a temperature/luminosity anomaly due to the fact that the luminosity of a star surrounded by a partial Dyson sphere would be lowered compared to a naked star of the same temperature. Conroy and Werthimer have searched by constraining the Jugaku infrared excess technique to older stars using a list of 1000 nearby older stars compiled by Wright and Marcy. Using older stars eliminates thick dust clouds around young stars. They also correlate with the rich K band near-infrared ground based data from 2MASS. They have found 33 candidates in the 12 μm IRAS band with 3 σ excesses from the mean.
The most recent investigation to be carried out appears to be the one using IRAS data by me and and my clleagues. The associated SETI search is still underway.
Dyson Sphere Search Bibliography
R. Carrigan, "The IRAS-based Whole-Sky Upper Limit on Dyson Spheres", Astrophysical Journal 698 2075-2086 (2009). It is available online at http://stacks.iop.org/0004-637X/698/2075.
For Dyson Spheres With Planck Spectrum Fits To IRAS",
Congress 2004 -
J. Jugaku, S. Nishimura, "A Search for Dyson Spheres Around Late-type Stars in the Solar Neighborhood" in "Bioastronomy 2002: Life Among the Stars, R. Norris and F. Stootman, eds, IAU Symposium, 213, 437 (2002) and earlier references cited therein
A. Globus, D. Backman, and F. Witteborn, "Searching for Partial-Dyson Spheres", preprint (2003
C. Conroy and D. Werthimer, "A Search for partial Dyson Spheres Around FKG Stars", preprint (2003) [popular description]
M. Y. Timofeev, N. S. Kardashev, and V. G. Promyslov, "A Search of the IRAS Database for Evidence of Dyson Spheres", Acta Astronautica Journal, 46, 655 (2000)