If advanced alien civilizations really exist, you would think they would be easy to find. A truly powerful alien race would stride through the cosmos like gods, creating feats of engineering the size of a star or a galaxy.
So instead of analyzing the spectra of exoplanets or listening for faint radio messages, why not look for the remains of celestial bodies, something too large and unusual to occur in nature?
The most common idea is that aliens can build something similar to a Dyson sphere. In their need for more powerful energy sources, an advanced civilization could harness the full output of a star.
They wrap a star in 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 looked for Dyson spheres in the Milky Way and found some interesting candidates.
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 special objects.
At first glance they appear to be M-type red dwarfs, but they have spectra that do not resemble simple stars. This kind of star-like infrared object is exactly what you’d expect from a Dyson bulb. But of course, extraordinary claims require extraordinary evidence, and that’s where things get sketchy.
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 look star-like, but are obscured by such a huge amount of dust that they emit mainly in the infrared.
And their spectra can be quite different from that of an M-type star. So the challenge is to distinguish between a hotDOG and a Dyson bulb. That’s where a new article on the arXiv comes in.
Rather than trying to specifically distinguish between the two, the authors instead look at the distribution of known hotDOGS. They found that statistically about 1 in 3,000 quasars are of the hotDOG type, so a broad search for Dyson spheres would likely include some dusty quasars.
The authors further note that any civilization powerful enough to build star-scale structures would also have the ability to obscure their infrared signal. We can’t just assume that aliens would build a Dyson sphere in such an obvious way. Overall, the authors say, the seven candidate superstructures can be explained by hotDOGs and other phenomena, meaning there is currently no clear evidence for extraterrestrial superstructures.
Source: www.universetoday.com
