A Dyson sphere was a colossal sphere constructed around a star, completely surrounding it. The interior of ...
A Dyson sphere was a colossal sphere constructed around a star, completely surrounding it. The interior of the sphere would absorb the entire energy output of that star, allowing for lifeforms to live on the interior surface almost indefinitely. Such a structure was theorized by the 20th century physicist Freeman Dyson.
Dyson sphere exterior
The Enterprise in orbit around the sphere
One of these spheres encased a G-type star and had a diameter of two hundred million kilometers (nearly the size of the orbit of Earth around Sol), giving it an internal surface area of approximately 250 million M-class planets. The exterior shell was composed of carbon-neutronium, and the interior was much like a habitable planet with various types of terrain and an atmosphere. The sphere was equipped with a portal with the diameter of several large starships which opened to allow ships to enter the interior, where there was enough room to orbit the star. Ships were guided through using tractor beam emitters triggered by subspace signals.
As no radiant sunlight or solar wind escaped from the sphere, starships were not able to detect it until they were almost on top of it. As a result, the USS Jenolan crashed onto it in 2294 after being pulled in by the sphere's immense gravity well while investigating it while en route to the Norpin colony. In 2369, the USS Enterprise-D discovered the Jenolan and investigated the sphere. The sphere was deserted because the star around which it was constructed was highly unstable. (TNG: "Relics")
It seems the designers of the discovered sphere did not take into account what would happen if the chosen star became unstable, or that they did, but it unexpectedly developed beyond their means or technology to stabilize it. This apparently highlights a flaw in such a design: without complete control of the star's output powering the sphere, any problems with it that cannot be overcome renders the entire sphere useless for habitation.