The Star Sea

The Star Sea was a galaxy that existed within the known universe. It contained approximately 400 billion stars, and most likely double that number of planets and moons. It was about 100,000 light-years wide from East to West edge, and about 80,000 light-years wide from North to South edge. It was orbited by a much smaller satellite galaxy known as the Kahal Nebula by the Eos, and featured a supermassive black hole at it's center. Branching out from it's core where two main spiral-arms, the Piephus Arm  and the Usinda Arm ; these two arms branched out further into other smaller arms.

Age
The Star Sea Galaxy was about 12 billion years old, making it relatively young among galaxies. About 500 million years after it's formation, it was nothing more than a vast elliptical cloud of stars with no shape or form to speak of. Eventually, about a billion years after it's birth, it began to form the famous spiral shape that it now contains. A majority of it's large stars were formed around the core or in many of the nebulas and star clusters, and star formation has largely halted by modern times (though not completely).

While an exact date is not known, the Star Sea snared the satellite galaxy known as the Kahal Nebula in it's gravitational pull some 4 billion years before modern times. The Kahal Nebula orbits the Star Sea in a wild elliptical pattern, going hundred of thousands of light-years out into intergalactic space to sometimes being so close that it could most likely merge with the Star Sea. However, no major collisions have taken place between the two galaxies, and the chances of star-to-star collisions would be miniscule should such a merge ever take place.

History
About one million years before the First Era,  the Eos  were in control of a galaxy-spanning empire which encompassed the entire Star Sea Galaxy. They were rumored to have control over millions of systems and an expansive wormhole-network for instantaneous travel between locations light-years away from each other. However, after a lengthy and unfortunate chain of events, they lost control over this vast empire and were reduced to controlling only a few dozen systems by the First Era. This left a large portion of the galaxy "unexplored" by First Era sentient lifeforms. The study of the Fall of the Eos Empire is a discipline of it's own.

The First Era marked the official fall of the Eos' Galactic Empire, The Eos themselves were stranded in one of their artificial worlds, Eos, unable to spread for some time due to hundreds of years of barbarism. This gave younger species a chance to grow, spread, and prosper, no longer hindered or controlled by the Eos, who were by now some of the only relics left over from the Dawn Era. During the First Era, many species gained the ability of space-travel, and began to uncover the vast Star Sea once more, spreading out to learn it's long forgotten secrets.