The Yggdrasil Star System is not a natural system - not in the sense that most of the systems within the galaxy are natural. The discovery of the Yggdrasil Star System was an accident caused by the mucking of interstellar coordinates with the mysterious Stygian Gates - possibly as an attempt to sabotage the expedition team that had been going out. The coordinates officially lead to no where - a blank chart of space in what was then the Outer Rim and which no known devices detected any signs of from any of the known planet's star maps. Something when wrong - and the ship jumped out of Stygian space and into a mysterious star system that was littered with shining particles that ran throughout the system.
Not knowing what it was they were dealing with, the expedition team made an effort to identify their location. Fortunately, a cabal of Free Council awakened had been on that expedition, and while they didn't initially know what they were dealing with, they had the means to study the Mystery in front of them and come up with an answer.
It took a few years charting through the system, but these mages came to unlock the name of this place, if nothing else: The Yggdrasil System. Composed of nine different planets orbiting between two stars - Yggdrasil and Ymir. These nine planets took up the names and many of the iconic features of the nine realms of ancient earth. Between these nine realms was the shining particles that connected the planets, which the cabal gave two names: The Star Road, or the Branches of Yggdrasil.
The Star System exists in a quantum state of existence, according to human science. Until recently, it did not even register to the strongest scanners (in fact, the planets and stars behind them were notable well before the system came into appearance on most Star Maps. Time does not seem to register the same here either, though the rules by which it flows are still being studied and considered dangerous. Individuals traveling to the Yggdrasil do not arrive at it in a linear fashion - records state that individuals traveling to it in the year 4000 have arrived anywhere between the years 3500 and 4500 - and these points in time seem to be unique to the individual. For instance - if one person leaves the Hastar Star System in the year 3927, and arrives 72 years in the future - they will return to their time when they leave and any future trips to the Yggdrasil system will be 72 years. If you've never traveled to or from your time distance will match anyone whose already traveled, but if no one has it seems to create a whole new distance of time - sometimes backwards, sometimes forwards. Researchers have attempted to see what happens when a group who always travels 72 years travels with a group which always travels 832 years. The answer has yet to be found, and at the moment the assumption is that the expeditions where this was attempted have all died, or at the very least are MIA.