The disk of the Milky Way is home to the vast majority of space dust and gas that exists in the galaxy. Also known as the "interstellar medium,” the gas and dust that floods the disk of the Milky Way comprise the majority of materials between the stars.
The gas in the Milky Way’s disk is primarily helium and hydrogen, and the sheer volume of space dust in the disk makes the majority of its regions opaque. That said, the most prominent feature of the disk region is its illuminated spiral arms. These regions are visible due to the seemingly countless number of hot young stars that comprise them.
The Milky Way’s disk is not a clearly-defined region of the galaxy. The disk does not possess clear-cut boundaries, and vast portions of it are blocked from visible wavelengths. Moreover, the absolute definition of the region is dependent on which objects are utilized to define it. As a result, astronomers often refer to multiple disks within the Milky Way Galaxy.
The Milky Way is a spiral galaxy with three distinct components: the disk, the halo and the core or nucleus. In addition to these regions, the Milky Way also contains at least three other components that cannot be seen by the naked eye.
These “invisible” areas include the galactic magnetic field, charged particles that encompass the galactic magnetic field and a ring of “dark matter” that is known from its immense gravitational influences.