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Picture this: You’re the emperor of an advanced alien civilization. For millions of years, your planet’s engineers have been building bigger and better gadgets: supercomputers, spaceships, flying cars, that sort of thing. All this ultra-tech makes life pretty fantastic, but it takes a lot of energy. Where is all that energy going to come from?

In 1937, the science fiction writer Olaf Stapledon imagined one answer: an enormous, spherical solar collector, built to encircle an energy-hungry civilization’s home star like a giant mylar balloon. This hypothetical mega-structure would grab every last photon of sunlight, providing enough energy to run whatever future technologies engineers could dream up. In 1960, physicist Freeman Dyson fleshed out the scheme: instead of a giant balloon, he speculated, an advanced civilization might crumble up its solar system’s uninhabited planets to create a swarm of rocks that could gather solar energy more efficiently. Dyson also pointed out that, if such a sphere or swarm existed, it would look to us like an unusually dark star, radiating waste heat in the infrared.

“Dyson spheres,” as they’re called (to Dyson’s chagrin), have become sci-fi staples. But they have also gotten some (semi) serious attention from scientists searching for evidence of intelligent life beyond Earth. In two studies, published in 2004 and 2008, Richard Carrigan, a researcher at Fermilab, searched for lopsided, infrared-heavy spectra among some quarter-million infrared sources in a database amassed by the IRAS satellite. IRAS, launched in 1983, surveyed about 96% percent of the sky. The result: no Dyson spheres–or, at least, none that he could confidently distinguish from other potential lookalikes.

If a civilization is sophisticated enough to build a Dyson sphere around one star, though, why should it stop there? Why not outfit a whole galaxy with Dyson spheres? As Jason Wright, assistant professor of astronomy and astrophysics at Penn State, wrote:

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