EU-Fic/Science/Physical Astrography
The Galaxy
The general term by which the denizens of the Star Wars civilization refer to its self-contained home. Actually consists of a single grand-design or semi-grand design (2-4 spiral arms) spiral galaxy, its globular clusters, and satellite dwarf galaxies, and other gravitationally bound structures.
The primary
The primary consists of the spiral galaxy itself. The spiral galaxy consists of three distinct morphological components characterized by orbits and stellar populations. The bulge, the disk, and the halo.
The bulge
The bulge is the superficial "hub" of the galaxy. At its heart is a supermassive black hole massing in the billions of main-sequence stellar masses, surrounded by a very dense collection of stars and stellar corpses and an accretion disk that produces high-intensity radiation and shreds star systems. The bulge is characterized by very old, dim red stars and stellar corpses, orbiting in near-circular orbits around the black hole at every orientation (hence why it appears as a sphere). The bulge is very low in post-helium elements and lacks warm main-sequence stars. The handful which do exist will be migrants from the disk where gravitational disturbances sent them spiraling inwards. Density increases directly proportionally with distance from the core. Near the edge of the bulge, it is intersected by the disk.
The disk
The most interesting portion of the galactic system, the disk is a population of younger stars in elliptical orbits confined to a single plane. The metallicity of the disk is higher than the other components, and the distance between high-metallicity stars is much lower, and also the rate of star formation. The spiral arms are not actual discrete phenomena but the product of density waves caused by "bunching up" of stars along their orbits; their close proximity makes the arms more dense, brighter, which in turn causes bouts of star formation, further brightening them with short-lived young star populations. The density of the disk increases inversely proportionally with radial distance from the core, with latitudinal distance from the plane of rotation, and directly proportionally with the spiral structure. The disk gradually diffuses outward and exists beyond its visible components further out.
The halo
The halo exists outside the disk and bulge. It consists of a sparse population of old stars in elliptical orbits at random inclinations. Most of these stars are old and dim, but a handful will be former disk stars ejected by gravitational perturbations. Many of the stars may be remnants from collision events.
The satellites
Globular clusters
These congolmerations of tightly-packed stars orbit the center of the galaxy and are mostly very old, red stars that formed at the beginning of the galaxy's formation. Their mellaticity is very low. Any high-metallicity stars were likely captured from the disk. The higher-metallicity clusters are generally associated with bulge (orbit closer in), and the lower ones with the halo (orbit further out). Their cores may be dominated by intermediate-mass black holes in the many thousands of stellar masses.
Satellite dwarf galaxies
These galaxies are similar to normal ones but they are small and have low stellar populations, and orbit close to the primary spiral. They have their own central black holes. Spheroidal, elliptical, and irregular dwarfs are more common than well-defined dwarf spirals.
Galactic remnants
These are semi-defined whisps of stars and gas and other material looping to and from the galaxy and through the halo, relics of collision events between the primary and its own satellites or interloping galaxies.
The dark halo
A massive structure surrounding the galaxy, the dark halo is a nebulous and nearly-unobservable body of matter that contains 95% of the mass of the galactic system. The halo mostly likely consists of a minority of dark, compact objects which are difficult to observe (MACHOs, like starless planets) and a great majority of nebulous particles which do not interact readily with normal matter, confounding detection and observability (WIMPs).
Astrographical Implications
The formation of complex life will hinge on stable star systems around main-sequence stars with high metallicity. These will almost all be found in the disk of the primary. High metallicity and star formation (found further inward in the disk and in the spiral arms) will be correlated with the best locales to extract raw materials (likely from planetesimals in protoplanetary disks before their accretion into high-gravity large planets). Stellar corpses will be important for possibly energy harvesting and the manufacture of sophisticated technology (like repulsorlift coils in black hole-based factories). They will be more common in globular clusters and the bulge, but will also exist in the disk. The economics of governance, trade in goods and services, immigrations, etc. will be fundamentally effected by the relative distance between hubs of resources and worthwhile systems of habitation. Therefore the inner areas of the disk will be most suited to the heaviest level of habitation and development, gradually declining outward (and inward) until there is no worthwhile economical places to go in the halo, and islands low-intensity civilization clinging to the edges of globular clusters or throughout high-metallicity and star formation-rich satellite galaxies like an island archipelago. Some low-intensity development of globular clusters and the less dense and easily accessible regions of the bulge for stellar corpse exploitation may occur.
The Deep Core refers to the bulge, but the known and settled parts are pretty much limited to the outer regions and fringes, and the areas of the disk intersecting the bulge. The inner areas are hazardous (high radiation and risk of collision), poorly charted (gravitational pertubations can constantly alter these already irregular, short-duration orbits), and mostly devoid of useful or economic resources or places of interest.
The Core Worlds consists of the spoke of the spiral arms around the bulge, and has the best economics for governance, industry, resource extraction, trade, etc. It is the social heart of the galactic society.
The Colonies and Inner Rim are like the Core Worlds but a bit more diffuse and further out; fundamental economics tends to make these areas incrementally poorer than the Core Worlds.
The Expansion and Mid Rim are middle areas of the galaxy where many of the indigenous civilizations may have originated (perhaps a higher rate of indigenous peoples and societies than the more astronomically violent and compact Core Worlds). These areas may take a poor-economics, quaint backwater culture with emphasis on old heritage.
The Outer Rim is the fringe of civilization. Consisting of the outer tenous reaches of the disk and the nearly orbiting satellites, it has some of the poorest economics and poorest physical fundamentals for close relations and development relative to the Core.
Wild Space is unincorporated territories and territories which do not fit traditional organization (distantly orbiting satellites, settled and well-known halo stars above or below the plane of the disk, recently resettled supernovae-effected regions, etc.).
The Unknown Regions are those astrographical locations now out of practical contact and association with the main civilization and economy. They are not correctly marked or known on astrogation charts, and are incapable of being reached. Mostly lost anonymous halo stars diffuse through the void around the galaxy.