The mystery of the possible Dyson spheres may be solved. First, a quick reminder on what Dyson spheres are:
"In their need for more powerful energy sources, an advanced civilization might harness the entire output of a star. They wrap a star within a sphere to capture every last photon of stellar energy. Such an object would have a strange infrared or radio spectrum. An alien glow that is faint and unique. So astronomers have searched for Dyson spheres in the Milky Way, and have found some interesting candidates."
Next the possible Dyson spheres:
"One major search was known as Project Hephaistos, which used data from Gaia, 2MASS, and WISE to look at five million candidate objects. From this they found seven unusual objects. They appear to be M-type red dwarfs at first glance, but have spectra that don't resemble simple stars. This kind of star-like infrared object is exactly what you'd expect from a Dyson sphere. But of course extraordinary claims require extraordinary evidence, and that's where things get fuzzy."
And how the mystery is solved (probably):
"Almost immediately after the paper was published, other astronomers noted that the seven objects could also be hot Dust-Obscured Galaxies, or hotDOGs. These are quasars, so they appear star-like, but are obscured by such a tremendous amount of dust that they mostly emit in the infrared."
So there you have it. Not Dyson spheres, hotDOGs.
Click through if you want to get the paper with all the details of what spectral bands were analyzed and how they were interpreted.
