Astroengineering

Engineered phenomena can also exist in space, from Dyson spheres to great stargates. The following megastructures are the work of Kardashev Type II civilizations at minimum.

At higher levels, stellar engineering and astroengineering can even allow a civilization to create or destroy stars and black holes, or, ultimately, entirely reshape galaxies to their needs. The very highest levels allow the manipulation of dark energy itself, and control over the very end of the universe.

Alderson disk. Proposed by Dan Alderson, this is a giant flat disc with a hole in the center in which sits a star. The hole is protected by a wall a thousand miles high to contain the atmopshere, and the outer edge reaches out 3-5 AU from the center. Life could exist on either side of the disk.

Artificial world. A planet-sized artificial world could either be a hollowed-out natural structure or a fully constructed metallic one. The surface and the interior could both be used for habitation.

Dyson sphere. A Dyson sphere is an artificial hollow sphere which completely encloses a star. The concept was proposed by the physicist Freeman Dyson in 1960, in which he suggested that an advanced civilization might use such a structure capture 100% of its star’s energy. Variations on the concept include Dyson swarms (billions of constructs orbiting in dense formation around a star), Dyson bubbles, and Dyson rings.

Ringworld. A ringworld is an artificial ring which encircles a star. It rotates to generate gravity, and has an inner surface which is populated. The area of such a surface would be equal to 3 million planets of Earth’s size.