If there really are advanced alien civilizations out there, you’d think they’d be easy to find. A truly powerful alien race would stride like gods among the cosmos, creating star-sized or galaxy-sized feats of engineering.

So rather than analyzing exoplanet spectra or listening for faint radio messages, why not look for the remnants of celestial builds, something too large and unusual to occur naturally?

The most common idea is that aliens might build something akin to a Dyson sphere. In their need for more powerful energy sources, an advanced civilization might harness the entire output of a star.

…

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.

And their spectra can be quite different from a M-type star. So the challenge is to distinguish between a hotDOG and a Dyson sphere. Which is where a new paper on the arXiv comes in.