The main issue of spin-gravity space habitats is that at some point the centrifugal force will overwhelm the tensile strength of the construction materials, even if perfect graphene were available. Thus, even the biggest spin habitats can't deliver more than a continents worth of living area per drum. One can of cause trade terrain features and gravity for more livable area, but even this has its limits.
Knowing that dynamically supporting a structure is usually the answer to get megastructures much bigger (think of atlas towers and dynamically supported orbital rings, which use mass stream technology), I was wondering if active support could be applied to Banks Orbitals and Ringworlds, which are usually considered impossible without unobtainium. Obviously, "materials" with high compressive strengths won't really help me here.
However the basic job of the spinning ring is to resist the centrifugal force. So what if we could compress the ring somehow to supply a counterforce. The main issue that arises from this is of cause that the friction between the ring, which will spin at hundreds of kilometers per second and basically anything, will have spectacular results. We would need a frictionless surface. For now, let's assume that the engineers got some kind of absolutely frictionless unobtainium coating. (maybe superconducting magnets could provide a frictionless interface?)
The basic design of such a structure would be a spinning ring around a central source of gravity and an encasing, slowly counter-rotating support mass. The support mass is well below its orbital velocity, thus it would fall down towards the gravity source. However, the spinning rings centrifugal force would balance out the forces.
I'm aware that the counter masses own gravity might become a problem at some point. At some point we might very well be dealing with a circumstellar donut planet, though I think the ring world would be the better bet from a construction materials point of view. I case the question comes up, where one would get the materials to build such a thing, this is pretty much per definition a K2+ project. So starlifting is on the table. And most of the support mass would most likely be metallic hydrogen stored in graphene and metal (what else to do with several planets worth of metals) containers.
The central object could be any of a number of options: a planet, gas-giant, star or black hole. It might very well be the power source of the whole structure, either a fuel depot, a Dyson Sphere or a Penrose Sphere.
I such a structure fundamentally possible? Did I mess up the physics somewhere? Could magnets handle the pressures of the interface?