The Milky Way isn't just a flat, spinning disk. It’s a 100,000-light-year-wide barred spiral of up to 400 billion stars, encased within an invisible sphere of dark matter.
At the center lies the galactic core, anchored by a supermassive black hole known as Sagittarius A*, which packs the mass of four million suns. Surrounding this black hole is the central bulge, a dense, peanut-shaped hub of ancient red and yellow stars.
Cutting through this central bulge is the galactic bar, a band of stars stretching about 27,000 light-years across. Rather than spiraling directly out from the core, the galaxy's arms originate from the ends of this central bar.
Extending outward from the bar is the galactic disk, a flattened region where most of the galaxy's gas, dust, and active star formation reside. This disk is organized into a distinct spiral pattern.
The Milky Way has two major spiral arms: the Scutum-Centaurus Arm and the Perseus Arm. These massive structures are densely populated with young, hot, blue stars and active star-forming regions. There are also several minor arms, such as the Norma and Sagittarius arms. Our Solar System is not located in one of the primary arms, but rather in the Orion Spur, a minor partial arm situated between the Sagittarius and Perseus arms, about 26,000 light-years from the galactic center.
Surrounding the flat disk is the stellar halo, a vast, spherical envelope containing scattered old stars and dense globular clusters. Beyond even this visible structure lies the dark matter halo. Though invisible, this envelope of dark matter makes up roughly 90% of the Milky Way's total mass, providing the gravitational glue that holds the spinning structure together.