What is a Dyson sphere?

Freeman Dyson suggested that a sufficiently advanced civilisation would need far more energy than a single planet provides and might build a swarm of satellites or a shell around its star to capture the star’s entire energy output. A rigid shell would be gravitationally unstable, so Dyson himself favoured a “Dyson swarm” of millions of orbiting solar collectors. A Dyson sphere would be detectable from afar because it would radiate waste heat as infrared light. Astronomers have searched for this infrared signature as a way to find advanced extraterrestrial civilisations. When the star KIC 8462852 (Tabby’s Star) dimmed erratically, some speculated about a Dyson sphere, though natural explanations are more likely.