Milky Way
The Milky Way is a barred spiral galaxy approximately 100,000 light-years in diameter, containing an estimated 100 to 400 billion stars. Our solar system is located within the Orion Arm, one of its major spiral arms, positioned roughly 26,000 light-years from the galactic center. The galaxy’s visible structure consists of a central bar, multiple spiral arms extending outward, and a disk composed of stars and interstellar gas. An extended halo of stars and dark matter surrounds these visible components, extending far beyond the main disk.
Dark Matter and Mass Distribution
Dark matter comprises the majority of the Milky Way’s total mass, distributed throughout the galactic halo and disk. This invisible matter is inferred from gravitational effects on visible stars and gas, which move at velocities inconsistent with the mass of visible objects alone. The nature of dark matter remains one of the fundamental open questions in physics, though various candidates have been proposed, including WIMPs (Weakly Interacting Massive Particles) and axions.
Central Structure
At the galactic center lies a supermassive black hole known as Sagittarius A*, which contains approximately four million solar masses. This object influences the motion of nearby stars and gas and may play a role in shaping the galaxy’s structure and evolution over cosmic timescales.
Source Notes
- 2026-04-24: Dark Matter WIMP · ▶ source
- 2026-04-12: JWST Detects Evidence of Universes Primordial Population III Stars in · ▶ source
- 2026-04-13: LHAASOs Confirmation The Universes Most Powerful Cosmic Ray Sources · ▶ source