Milky Way

The Milky Way is our galactic home—a vast, rotating disk of roughly 100–200 billion stars, held together by gravity and threaded through by dark matter. Named for its milky appearance in Earth's night sky, it spans about 100,000 light-years across and rotates as a unified system, though not rigidly: Orbital mechanics govern how stars orbit the supermassive black hole at our galactic center.

The Milky Way contains stars of every age, massive stellar nurseries where new stars ignite, and remnants of ancient cosmic events. From our vantage point within one of its spiral arms, we see it edge-on, a luminous river dividing our night sky. Gravitational lensing and observations of distant objects have revealed much of its hidden structure.

The galaxy likely formed roughly 13.6 billion years ago, soon after the Big Bang. It continues colliding very slowly with the Andromeda Galaxy, a merger expected billions of years hence. Understanding the Milky Way illuminates how cosmic forces organize matter at the largest scales.

Related

Galaxy, Stars, Cosmic dust, Stellar formation, Dark matter, Space exploration