The Fermilab Phase I IRAS filter-based search for Dyson spheres was reported at the International Astronautical Congress in Vancouver in 2004. A link to the paper is on the right. A more sophisticated search using the IRAS Low Resolution Spectrometer (LRS) has now ben reported (see June 2 Power Point on right). The Phase II technique follows the Dyson Sphere search excercise for amateurs page.
Particle astrophysics seminar - Fermilab - Jun 2 2008 (Power Point-1M)
The Fermilab search has now been published in Astrophysical Journal 698 2075-2086 (2009). It is available at http://stacks.iop.org/0004-637X/698/2075.
Sources were discarded if the IRAS flux quality factors FQUAL(i) for the 12 and 25 μm only corresponded to an upper limit . This left 10982 sources. Requiring a signal in the 60 μm filter limited the possible upper temperature range since a high temperature Dyson Sphere might not give a signal in the 60 μm filter. For this reason and temperature limits on carbon-based life the search focused on a temperature range of 100 to 600 °K (see below) leaving about 6521 sources. No cut has been made on proximity to other sources. By doing this partial Dyson spheres were not ruled out. The IRAS database also includes the variables VAR, an indicator of source variability. VAR was not used as a cut since a Dyson Sphere might be eclipsing a nearby companion in a multiple star system.
There is a significant presence of emission in the IRAS 100 μm band on a wide range of angular scales due to so-called infrared cirrus from interstellar dust. Zodaical light can also be a problem. The cirrus in the 100 μm filter is often well above a Planck fit to the lower three filters. The IRAS 100 μm filter was not used for fitting for this reason. Parenthetically, the 60 μm filter also sometimes sees cirrus.
The source temperature was determined via a least squares fit:
where Ci are the Calgary corrected spectral values, an is a normalization factor, and Pνi is proportional to the blackbody spectrum as a function of frequency that is a function of temperature.
The source distance is needed to establish the absolute luminosity and show that the infrared power correspnds to a characteristic power or absolute luminosity for a typical visible star. A distance determination could be done by finding a Dyson Sphere that was a member of a binary thereby allowing a red shift measurement for the other member, by associating the Dyson Sphere with a cluster at a known distance like the Pleiades or the galactic center, by using a kinematic distance determination, or by measuring the red shift for a partial Dyson Sphere. No source distance determination was made for the Phase I search.
Phase I showed that less than 1 in 600 of the IRAS sources were clustered within about 10% of the blackbody line. During Phase I it became clear the Low Resolution Spectrometer data with many more points in a spectrum could give more definitive fits. That approach is now being pursued in Phase II.
As noted on the Dyson Sphere look-alike page there are several natural surrogates that may be difficult to rule out. In addition it is clear that both pure and partial Dyson Spheres are possible. Further, there might be several shells at different radii leading to multiple Planck distributions. WE ARE NOW LEARNING MORE QUESTIONS TO ASK ABOUT DYSON SPHERES!