Structure and Components: Anatomy of Our Galaxy

The Milky Way's structure resembles a cosmic fried egg – if that egg were 100,000 light-years across and spinning once every 225 million years. At the center lies the galactic bulge, a football-shaped region packed with old, red stars. This dense core, about 10,000 light-years across, harbors our galaxy's supermassive black hole, Sagittarius A*, weighing 4 million times our Sun's mass.

Surrounding the bulge is the galactic disk, where our Sun resides. This thin disk, only about 1,000 light-years thick, contains the galaxy's spiral arms and most active star formation. The disk isn't uniform – it's warped like a vinyl record left in the sun, likely due to gravitational interactions with satellite galaxies. Gas and dust concentrate in the disk, providing raw material for new stars and planets.

Recent observations revealed that the Milky Way is a barred spiral galaxy, not just a simple spiral. A bar-shaped structure of stars extends from the central bulge, with spiral arms emerging from its ends. This bar, about 27,000 light-years long, acts like a cosmic mixer, stirring up gas and triggering star formation as it rotates.

The spiral arms – including the Perseus, Sagittarius, and Scutum-Centaurus arms – aren't solid structures but density waves. Like traffic jams that persist while individual cars move through them, spiral arms are regions where stars and gas bunch up temporarily. Our Sun resides in a minor arm called the Orion Spur, located between the Perseus and Sagittarius arms.

Enveloping everything is the galactic halo, a roughly spherical region extending far beyond the visible disk. This halo contains ancient globular clusters – dense balls of hundreds of thousands of old stars – and is dominated by invisible dark matter. The dark matter halo extends at least 300,000 light-years from the center, containing six times more mass than all visible matter combined.