Milky Way.

The Milky Way galaxy is a vast grouping of several hundred billion stars, gas, and dust to which the Sun and solar system belong. All the stars visible to the unaided eye in the night sky are a part of this same huge collection. Most of the stars, gas, and dust observed in our galaxy are contained in a thin disk more than 100,000 light-years in diameter, with a lens-shaped bulge at its center. This central bulge, also called the galactic nucleus, contains the greatest concentration of stars and, right at its center, a supermassive black hole. Within the disk are several spiral arms in which new stars form. Surrounding the disk and central bulge of our galaxy is the roughly spherical galactic halo, a few hundred thousand light-years in diameter, sparsely populated with old stars and old star clusters but with virtually no gas or dust. The Sun and solar system are located in the disk, within one of the spiral arms or arm branches, about 26,000 light-years from the center. It takes the Sun and solar system more than 200 million years to complete one orbit around the galactic center.