Final answer:
The Milky Way Galaxy has a complex structure with a spiral pattern, involving a thin disk, spherical halo, and a central supermassive black hole. Our Sun resides within one of the spiral arms, and the Galaxy features differential rotation which contributes to its spiral shape. Most of the Galaxy's mass is dark matter, detectable only through gravitational effects.
Step-by-step explanation:
Milky Way Galaxy Structure and Dynamics
The Milky Way Galaxy is a majestic structure composed of a thin disk with dust, gas, and stars, enveloped by a spherical halo containing ancient star populations and globular clusters. A peanut-shaped nuclear bulge lies at the center along with a supermassive black hole. The Sun is situated roughly 26,000 light-years from this center, within one of the Galaxy's spiral arms. Understanding this was greatly aided by comparing our Galaxy with similar spiral galaxies, like Andromeda.
Galaxies like the Milky Way develop their spiral structure over billions of years. The gaseous, spiral pattern emerges from differential rotation, where stars closer to the center orbit faster than those farther away, just as Kepler's third law describes. This rotation sculpts the Galaxy's distinctive spiral arms, as material in larger orbits trails behind that in smaller ones. Our Sun is located in a spur off one of these spirals.
The mass of the Milky Way is estimated to be about 2 × 10¹² Msun (solar masses), with as much as 95% constituting dark matter in the halo. This elusive dark matter can only be detected through its gravitational interaction with visible matter. The Sun's journey around the Galaxy takes roughly 225 million years, known as a galactic year, a testament to the vast scales involved in cosmic timelines.