"This is a thing that cannot be; and yet it is. Nothing known to all the races of the stars can build a Dyson sphere, but here, somehow, someone did."
"Ask anyone with an understanding of modern material science and the laws of physics; they’ll tell you such a thing is impossible. The sphere, they will tell you, was a clever hoax to draw dupes and victims to some clever lunatic’s scheme to get rich. The images and videos were artificial, contrived, full of obvious glitches and artifacts.
These people have never seen the great Sphere on the fringe of the galaxy; a nameless star burning at the heart of it. Certainly, lesser spheres exist; clouds of sattelites, solar-sail shrouds that entrap the full radiance of a sun, even the strange ringworlds of lost eras. None, however, can compare to the Great Sphere."
Dyson Spheres, as the structures are known among humankind, were thought of by Freeman Dyson in 1959; the idea of a massive cloud of energy collectors to fuel the advance of civilization, completely enclosing a star to utilize the energy available. Many other races have thought of these constructs, and to a degree, some have been built. Generally, these are complex arrays of sattelites, carefully arranged to soak up as much energy as possible while dealing with the complexities of gravity and orbital mechanics. A few races, having discovered the trick of manufacturing solar sails, have enshrouded stars in improbably vast swathes of the stuff, hanging their civilizations from the interior like improbable fruit. One civilization extinct in the modern era even managed to partially solve the structural issues of solid-state spheres sufficiently to build immense ringworlds capable of supporting immense populations.
Until the discovery of the Great Sphere on the very edge of the Sagittarius Arm of the Milky Way, however, it was believed impossible to make a Dyson Shell - an immense, solid sphere completely enclosing a star, kept in position around the fusion furnace. Such construction was beyond the ability of material science; the ability for it to keep station with the star was mind-boggling to even consider, with the amount of power required.
Then, unexpectedly, an automated probe wandering the outer fringes of the galaxy, looking for relics of the past eras of galactic civilization and valuable resources that might have escaped the competition of the worlds in denser regions, discovered an anomalous object; unable to match the profile of it to anything known, and the limited AI aboard it incapable of understanding what it was beyond ‘no immediate threat’, it documented the rough location and sent a report back to civilization.
The report, when it was processed, was at first considered a glitch; it was forwarded to the technicians who were responsible for fixing such errors, to resolve what the probe had actually found.
The technicians, a short while later, responded that while they had no clue what it was, there weren’t any glitches involved.
The uproar was immediate, massive, and engulfed most of civilized space with shock and amazement. Governments demanded to know who was responsible for it, and when no one stepped forward, began to level increasingly absurd accusations. The public and the marvels of mass communication only made matters worse; rumors abounded that it was an alien artifact from outside the galaxy; it was a weapons platform; a massive superbomb that would destroy everything; a prison for some kind of super-powerful Thing; and many more, each more ludicrous than the last.
Given the immense distance involved - even for a galactic civilization, travel to the most remote outskirt of the galaxy, without any readily obvious source of fuel at the end of the trip, was a difficult prospect at best - few missions were even planned to the anomaly, and fewer still were launched.
In the end, only one arrived at the site the probe had found the anomaly. The others fell prey to the various hazards of such long-distance journeys; rumors, however, circulated that they had been destroyed by the object when each failed to report in.
What the one successful group found blew anything the rumor mill had circulated clean out of galactic orbit. It was, the reports said, a Dyson shell; one comprised not of solar sails strung with habitats, but a solid shell of matter nearly a hundred kilometers in depth, unlike anything witnessed before. Immense plates of matter, crushed to impossible densities, were arranged along an immense framework of exotic matter, unlike anything ever seen or predicted by science. More astonishing than that, the structure had ports - vast openings that could swallow a Titan-class superdreadnought with ease, with a massive airlock structure that irised open at the approach of the scout vessels - a process, caught on video, that took nearly thirty minutes - to admit them to the Sphere’s interior via a gargantuan airlock.
Inside, one of the scouts later said, was Light. A G-class star, perhaps a little cooler than the one that humanity’s homeworld orbited, hung in the heart of a sphere of solid matter, in an open space nearly five AU across. The distances involved defied comprehension; the sapient minds aboard the vessels spent the time in a near-trance awestruck by the Sphere. Only the automatic functioning of the ship, managed by the not-quite-aware expert systems, permitted them to navigate the interior, recording all the information possible before finally departing several days later; indeed, only the automatic functions of the ships permitted the crews to survive. The collective trance, broken as soon as they exited the Sphere’s interior, had left them unable to attend to their own needs; almost uniformly, the entire crew had been taken, one by one, to the ship’s automated medical facilities and cared for as they collapsed.
Between those, neatly sectioning the sphere’s inner surface off in massive grids, was the exotic matter framework supporting the entire thing. It shone, more brightly than the star itself, in colors that seemed to slip between anything that could be named by any species. The temperature readings were equally bizarre; one reading indicating temperature far in excess of the fusion point, while the next moment the reading indicated the material bordered on absolute zero. It was, in a word, impossible. Much of the recorded information could be described thus; the entire Sphere was a place where the known laws of existence seemed not to work the same way, from the effects on the crews’ minds to the bizarre superstructure of exotic matter.
The information, when delivered, was instantly locked down; those few fragments allowed to slip out were rapidly decried as falsehoods, forgeries designed to fool the gullible. Thr truth, according to official release, was that what had seemed an immense structure was little more than a dense clot of interstellar gas; seen from the right (or wrong) angle, it gave the impression of an immense construction. Many people, conditioned to belief in authority, accepted this blindly. Others, less sanguine about the words of those in charge, analyzed the stray images and materials themselves. Rumors remained that perhaps something really did exist out there on the galactic fringe. The crew of the exploration team almost all vanished, save for a few who had, following the ancient instincts of impending doom, escaped before the ships returned, jettisoning themselves in escape pods as soon as they reached the edges of civilized space. Those few were behind many of the rumors - mostly trying to scrape together enough funding to take another trip to the Great Sphere, one better equipped to handle what had been found.
Every now and then, since the scout ship returned, another ship launches with a deliberately vague destination before vanishing off into the great void, headed in the general direction of the Sagittarius Arm’s outermost fringes; none are known to have ever returned.
The location of the Great Sphere is at the very fringe of the galaxy itself, out in the halo of dust and gas; if it were readily visible, the star within it would mark the farthest point that could realistically be considered to be ‘within’ the galaxy in the direction of the Sagittarius Arm.
The Sphere itself contains a single G-class star, luminous output slightly cooler than Sol; the exterior of the Sphere is only a few tens of degrees above the background radiation level. Somehow, the Sphere consumes or stores tremendous amounts of energy, enabling the internal temperature to remain at a livable temperature.
The exterior of the sphere is ridiculously dense; crushed almost to white dwarf densities, an analysis suggests that it might be largely comprised of iron, although the exotic matter underneath it provide an array of anomalous energy sources and bizarre distortions of local spacetime. Located at half a dozen points around the vast bulk of the equator are immense gateways; these automatically begin to open whenever any vessel bearing a sentient lifeform approaches within five hundred thousand kilometers, the process taking a full half-hour to accomplish; the opening, at maximum, is fifty thousand kilometers across; vast, but a mere pittance compared to the construct itself. These lead into a tunnel through the sphere’s hundred-kilometer shell of degenerate matter; ships inside must wait for the exterior doors to close before the interior opens before them, permitting the light of the enclosed star to flood in.
Should a sapient manage to resist the Sphere’s internal effects, or review automatic recordings afterwards, the interior of the Sphere is revealed to be at least as unlikely as the exterior. First, the framework of exotic matter is visible all around the sphere, glowing in nameless colors that are unsettling to witness. Attempts to study this material will yield confusing, contradictory data: it appears to fluoresce in every spectrum, from the deep radio frequencies to the improbably high energies of gamma radiation and cosmic rays, but does not yield energy in the process - the emissions are ‘ghostly’ in some bizarre fashion; temperature scans will yield wildly divergent values, ranging to the furthest extremes of what the sensors can handle, including ‘impossible’ values, such as colder than absolute zero; active sensors are unable to detect the substance at all, with emissions directed at it being absorbed completely. Other scans yield equally impossible results - checking mass/gravity returns values beyond the density of a singularity, a lack of mass sufficient to be one of the great voids between galactic superclusters, and an antigravitic/anti-mass that should hurl the entire sphere apart at nearly the speed of light. The only two consistent traits of the material are the bizarre hues of the luminescence and that physical material other than the degerate matter of the shell, approaching within a few hundred yards, will begin to experience a repulsion effect; the force grows exponentially stronger as one approaches, essentially making direct contact impossible.
By comparison, the spaces between the framework are almost too normal. Vast swathes around the framework are given over to massive metallic arrays that are aimed at the enclosed star, apparently collecting and storing the solar energy for some unknown purpose. Further in, ringed by these massive metallic forests, there are biospheres of improbable size. In them, vast numbers of creatures dwell in improbably diverse environments and wildly divergent biologies. None of the creatures have achieved sapience, although numerous exist which might be ready to be uplifted.
The construction of the Great Sphere is literally impossible; were it not for the framework of exotic matter holding the sphere’s normal-matter plates in place, the entire thing would buckle and break apart in short order. http://www.nada.kth.se/~asa/dysonFAQ.html contains more information about Dyson spheres of all kinds; the Great Sphere is a rigid-shell construction.