Milky Way Galaxy

The Milky Way Galaxy, commonly referred to as just the Milky Way, or sometimes simply as the Galaxy, is the galaxy that Mankind calls home and in which the Imperium of Man and all of the other starfaring intelligent species known to humanity are located. The Milky Way is a barred spiral galaxy that is part of the Local Group of galaxies. It is one of hundreds of billions of galaxies in the observable universe. Its name is a translation of the Latin Via Lactea, in turn translated from the Galaxias, referring to the pale band of light formed by stars in the galactic plane as seen in the night skies of Terra.

Some sources hold that, strictly speaking, the term Milky Way should refer exclusively to the band of light that the galaxy forms in the Terran night sky and the skies of many other settled planets, while the galaxy should receive the full name Milky Way Galaxy, or alternatively the Galaxy. However, it is unclear how widespread this convention is, and the term Milky Way is routinely used in either context.

The stellar disk of the Milky Way Galaxy is approximately 100,000 light-years in diameter, and is considered to be, on average, about 1,000 light years thick. It is estimated to contain at least 200 billion stars and possibly up to 400 billion stars, the exact figure depending on the number of very low-mass, or dwarf stars. This can be compared to the one trillion stars of the neighbouring Andromeda Galaxy. The stellar disc does not have a sharp edge, a radius beyond which there are no stars. Rather, the number of stars drops smoothly with distance from the centre of the galaxy. Beyond a radius of roughly 40,000 light years, the number of stars drops much faster with radius, for reasons that are not understood.

Extending beyond the stellar disk is a much thicker disk of gas. The gaseous disk of the Milky Way has a thickness of around 12,000 light years. The Galactic Halo extends outward, but is limited in size by the orbits of two Milky Way satellites, the Large and the Small Magellanic Clouds, whose perigalacticon is at about 180,000 light years. At this distance or beyond, the orbits of most halo objects would be disrupted by the Magellanic Clouds, and the objects would likely be ejected from the vicinity of the Milky Way.

History
Little of the vast history of the galaxy has been revealed to Mankind. What is known beyond the dimly-remembered confines of even humanity's own story has largely been drawn by various human scholars and Adepts of the Adeptus Mechanicus from ancient xenos ruins scattered across the stars and the dying Infinity Circuits of shattered Eldar Craftworlds.

Birth of the Star Gods
The birth of the entities known as the Star Gods occurred at the same time as the moment of Creation itself, as they formed from the vast, insensate energies first unleashed by that churning mass of cataclysmic force. In that anarchic interweaving of matter and energy, the sea of stars began to swirl into exitence and for an eon the universe was nothing more than hot hydrogen gas and light elemental dust ruled over by the gravitic force of billions of newborn suns. Long before the first planets had formed and cooled, the very first truly self-aware beings emerged, their thoughts encased within the lines of force produced by the plasma and electromagnetic flares of the stars themselves. In later times, these entities would become known as the C'tan, but early in their existence they were nothing like the malevolent beings they would eventually become. They were little more than monstrous energy parasites that suckled upon the solar energies of the stars that had brought them into existence, shortening the lives of otherwise main-sequence stars by millions of standard years. In time, these star vampires learned to move on the diaphanous wings of the universe's electromagnetic flux, leaving their birthplaces to drift through the cosmic ether to new stellar feeding grounds and begin their cycle of stellar destruction once more. Beings of pure energy, they paid no mind to the hunks of solid matter they passed in the vacuum of space, the blazing geothermal fires and weak geomagnetic fields of these nascent planets insufficient to be worth feeding even their ravenous hunger.

The Empire of the Old Ones
Just as the stars gave birth to their children so the planets of the newborn galaxy eventually gave birth to lifeforms composed of matter which began the long evolutionary climb to self-awareness. The first sentient beings of the Milky Way Galaxy known to have developed a civilisation technologically advanced enough to cross the stars was a reptilian race of beings called the Old Ones by the Eldar, who knew them best. They possessed a slow, cold-blooded, but still deep wisdom, having long studied the stars and raised astronomy and physics to such a level that their science and technology appear to humanity like an arcane art. Their understanding of the workings of the universe were such that they could manipulate alternate dimensions and undertake great works of psychic engineering. Their science allowed them to cross the vast gulfs of space with only a single step through the myriad Warp Gates they built to connect the worlds of the galaxy in a vast network much like the Eldar Webway of today, though on a much larger scale. The Old Ones spread their spawn to many places in the galaxy, but they also knew that all life was precious. Where they passed, they seeded new intelligent species and reshaped thousands of worlds to make them their own according to their predetermined environmental and geographic criteria. It is believed by some in the Adeptus Mechanicus that even Terra felt the Old Ones' touch long before humanity's rise to self-awareness, though this notion is considered heretical at best by the Ecclesiarchy.

The Necrontyr
As the Old Ones spread across the galaxy, younger, fiercer intelligent races struggled upwards in their wake. The Necrontyr were one such species, born on a world scourged by an unstable star that drove their evolution forward with atomic winds, solar flares and plasma storms. What little information the Imperium has on the Necrontyr tells that their lives were short and uncertain, their bodies blighted and consumed at an early age by the terrible cancers and other illnesses linked to the high levels of ionizing radiation given off by their sun. Necrontyr cities were built in anticipation of their citizens early demise, as the living were only brief residents living in the shadow of the vast sepulchres and tombs of their ancestors. On the Necrontyr homeworld, the greatest monuments were always built for the dead, never the living. Unable to find peace on their own world, the Necrontyr blindly groped outward into the universe to explore other stars. Using stasis crypts and slow-moving, sub-light, antimatter-powered torch-ships that were clad in the living metal known as necrodermis to resist the millennia-long journeys through the void, the Necrontyr began to colonise distant worlds. Sometime during their slow expansion, the Necrontyr encountered the Old Ones. The colonisation of much of the galaxy by the reptilian mystics had been immeasurably swifter and more expansive than that of the Necrontyr because of their Warp Gates and mastery of the Immaterium. That, and the Old Ones' incredibly long, if not downright immortal lifespans, kindled a burning, jealous rage in the Necrontyr, which ate at their culture spiritually as much as their physical cancers consumed their bodies. The Necrontyr were astonished to learn that another intelligent species enjoyed such long lives while their own were cut so brutally short. As their surprise turned to jealousy and then hardened into hatred, the Necrontyr turned their entire civilisation towards destroying the Old Ones and all of their spawn across the galaxy.

The War in Heaven
The terrible wars between the Old Ones and the Necrontyr that followed would fill a library in their own right, but the Necrontyr could never win. Their superior technology was consistently outmanoeuvred by the Old Ones thanks to their mastery of the Webway portals and Warp Gates. The Necrontyr were pushed back until they were little more than an irritation to the Old Ones' dominance of the galaxy, a quiescent threat clinging to their irradiated world among the Halo Stars, exiled and forgotten. The Necrontyr's fury was cooled by their long milllennia of imprisonment on their homeworld, slowly transforming into an utter hatred towards all other forms of intelligent life and an implacable determination to avenge themselves upon their seemingly invincible enemies.

From the earliest days of their civilisation, Necrontyr scientists had been deeply engaged in stellar studies to try and understand and protect themselves from their own sun's baleful energies. After long, bitter centuries of searching fo some power to unleash upon the Old Ones, the Necrontyr researchers discovered unusual electrodynamic anomalies in the oldest, dying stars of the galaxy. In the complex skeins of the energetic plasma of these suns, the Necrontyr found a sentience that was more ancient than that of any of the corporeal species in Creation, including the Old Ones, entities of pure energy that had spawned during the birth of the stars eons before. These entities had little conception of what the rest of the universe entailed when the Necrontyr first found them, feeding upon the solar flares and magnetic storms of these bloated red giants. Here was the weapon the Necrontyr had long sought to bring about the downfall of the Old Ones, beings they believed were the progeny of the death-god they worshipped.

The power of these star-born creatures was incredible, the raw energy of the stars made animate, and the Necrontyr called them the C'tan or "Star Gods" in their own tongue. The C'tan were dispersed across areas larger than whole planets, their consciousnesses too vast for humanoids to comprehend and how the Necrontyr managed to communicate with them is unknown to the Adeptus Mechanicus. Understanding that such diffuse minds could never perceive the material universe without manifesting themselves in a materal form, the Necrontyr forged physical shells for them to occupy, cast from the necrodermis living metal they had once used for their colony torch-ships. Fragmentary Eldar legends tell of translucent streamers of electromagentic force shifting across space as the star vampires coiled into their new bodies in the physical realm acoss an incorporeal bridge of starlight.

Incomprehensible forces were compressed into the living metal of the necrodermis bodies which the Necrontyr had forged as the full power of the C'tan at last found form. As the C'tan focused their consciousnesses and became ever more focused on their new mode of existence, they came to appreciate the pleasures of being beings of matter and the other realties of corporeal life. The deliciously focused trickles of electromagnetic energy given off by the phycial bodies of the Necrontyr all about them awakened a new hunger in the C'tan very unlike the one they had once sated using the nourishing but essentially tasteless energies of the stars.

For their part, the Necrontyr soon fell into awe of their discoveries anf the C'tan moved to take control over their benefactors. The powers of the C'tan manifested in the physical world were indeed almost god-like and it was not long before the C'tan were being worshipped as the Star Gods the Necrontyr had named them. Perhaps they had been tainted by the material universe they had become a part of, or perhaps this had always been their nature even when they were bound to the suns they fed upon, but the C'tan proved to be as cruel and capricious as the stars from which they had been born. They soon revelled in the worship of the Necrontyr and feasted upon the life energies of countless mortal slaves.