Skyriver

Skyriver was one of the billions of galaxies that existed in the universe. Composed of about 400 billion stars and over 3.2 billion habitable systems in a disk 120,000 light-years in diameter, the galaxy was orbited by seven smaller satellite galaxies, of which five were directly accessible by the time of the Galactic Empire. The galaxy was home to between five and twenty million sentient species, and over one hundred quadrillion sentient beings lived in one billion star systems, interacting with each other through travel, diplomacy, trade, politics, and war. In historical memory, this galaxy had been ruled by the Galactic Republic, the Galactic Empire, the New Republic, and the Galactic Federation of Free Alliances, the Fel Empire, Darth Krayt's Galactic Empire and was home to the Force-using orders of the Jedi and the Sith.

Astrography
The galaxy was between 100,000 and 120,000 light-years across, or 37,000 parsecs (a parsec is 3.258 light years), and approximately 13 billion years old. The galaxy's luminous disk contained some four hundred billion stars, of which around a quarter had been properly surveyed by the galactic community by the time of the Galactic Empire. The luminous disk revolved around the Galactic Center, a supermassive black hole that massed as much as four million suns. As late as the Declaration of a New Order, only probe droids had ever visited the black hole at Galactic Center.

The galaxy bulged around The Galactic Center to form a bright sphere known as the Deep Core. This region was around seven thousand light-years across and contained some thirty billion tightly-compacted stars. Towards the center the stars of the Deep Core were only around a hundredth of a light-year apart, and were known to collide and rip out each other's stellar cores. Most of the stars of the luminous galaxy were in a disk of spiral arms rotating around the Deep Core. Galactic civilizations named four spiral arms: the Bakchou Arm, the Ettarue Arm, the South Arm, and the Tingel Arm. The brightest supergiant stars were concentrated in the spiral arms, as well as glowing clouds of gas and dust, which contributed to the apparent gaps between the arms even though those areas were full of stars.

Most stars were within a thousand light-years above or below the plane of the luminous disk, forming a two thousand-light-year region known as the "thin disk". For three thousand, five hundred light-years on either side was the "thick disk", which was poorer in stars than the thin disk and even fewer of these had a system of planets.

Stellar Halo
Beyond the thick disk was the stellar halo, a huge sphere surrounding the entire galaxy with a few billion stars in highly elliptical orbits. Nearly two hundred globular clusters orbited in this region. The globular clusters were typically lifeless, packing hundreds of thousands of extremely old, inhospitable stars into only a hundred light-years. Many of the globular clusters, however, were considered extremely beautiful sights, such as Cosm's Well.

The galaxy was orbited by seven dwarf satellite galaxies, some of which contained twenty billion stars. They were ranked in order of distance. The closest was Companion Aurek, also known as the Rishi Maze, a complex tangle of stars high above the galactic plane. Companion Besh, also known as Firefist, was some 150,000 light-years away from the galaxy and had only ever been surveyed by probots. The other satellite galaxies, Companions Cresh through Grek, were much further out. Most of the Companions were described as having ancient, metal-poor remnants of stars and not much life.

A hyperspace disturbance beyond the edge of the galaxy severely complicated hyperspace travel outside the disk and generally discouraged extra-galactic exploration. A band of whorls and eddies that spun around the galaxy too quickly to be traversed at faster-than-light speeds, a number of astrophysicists believed this to be a creation of a mysterious ancient race known as the Celestials. Beyond the galaxy's rim, separating it from other galaxies, was a vast expanse of starless space known as the Intergalactic Void.

History
The history of the galaxy has unraveled for untold millennia. The development of civilizations in all of its regions was not only influenced by physical geography, but also by urban geography and architecture, as inhabitants sought to put their own stamp on the worlds in which they inhabited.

Formation
Some thirteen billion years before the Battle of Yavin, an immense cloud of gas and dust collapsed under its own gravity and coalesced to form a revolving disk, creating the galaxy. Over many more billions of years, the stars and planets began to form. About 8 million years after the formation, life had begun to evolve in the galaxy, with some of the earliest examples of non-sentient life developing on Goroth Prime.

Around 3 million years latter, many of the galaxy's most well-known species were evolving: the Wookiees began on Kashyyyk as a species of tree-climbers. The Oracle of Pelgrin, quite possibly the oldest artifact in the galaxy, was believed to date from this period. By 200,000 years before the Battle of Yavin, the Zhell, possible ancestors to the Humans, had developed intelligence and were waging war against the Taungs for control of their mutual homeworld of Notron, later known as Coruscant.