In the 60s, Freeman Dyson proposed that as intelligent life grew beyond the resources of a planet, it could re-engineer local solar system matter to create orbiting satellites which would be able to use more of their sun’s free energy. The result would be that looking at a star, it would appear dimmer, and in the extreme, invisible, and instead you would see the re-radiation of infra-red light from the satellites.
The Dyson sphere is a specific case of the inevitable thermodynamic result of the phenomenon of life. Without life, a star radiates high energy photons, which are re-radiated by a planet as many more low energy infra-red photons, with a black body distribution at around room temperature. This results in an increase in entropy. The localized, low entropy order of living things, act as little entropy machines which accelerate the overall production of this entropy.
In other words, no matter how weird the Dyson sphere sounds, it is a viable example of the mechanism by which the inevitable extreme increase in entropy (from the waste of a low-entropy grabbing, industrial society, operating for any significant period of time), could be achieved. There might be others, but they will all result in the same thing – low temperature black body spectrum waste.
For the first time, using the IRAS infra red telescope, a serious search has been conducted for Dyson Spheres, or dim stars, and the results are essentially negative. There are a few candidates but it is very difficult to differentiate them from specific cases of Red Giants or glowing, stellar heated, dust clouds.