Star Trek: The Farthest Star Wikia

The Milky Way is a spiral barred galaxy of roughly 100,000 light years in diameter and containing 400 million stars. It is split into three areas, the core, the disc and the halo.

The Milky Way is completely surrounded by an energy barrier called the Galactic barrier. At the centre of the galaxy is another barrier. These barriers can pose a danger to interstellar craft trying to traverse through them.[1][2]

The Federation splits the galaxy into four equal sized quadrants, Alpha, Beta, Gamma and Delta Quadrants.