十万个为什么·科学启蒙30篇（3）

3 / 30

银河系是什么

The Milky Way is our home galaxy—a vast, rotating disk of over 100 billion stars.
It looks like a hazy band of light across the night sky because we see it edge-on from inside.
Our Solar System sits about 27,000 light-years from the galaxy’s dense, star-packed center.
Most stars, including the Sun, orbit the galactic center once every 225–250 million years.
A supermassive black hole named Sagittarius A* lives at the very heart of the Milky Way.
Dark matter makes up about 90% of the galaxy’s total mass, though we cannot see it directly.
Spiral arms—like the Orion Arm where Earth resides—contain young stars and glowing gas clouds.
The Milky Way is slowly merging with the smaller Andromeda Galaxy, a process that will take billions of years.
Radio telescopes help map its structure by detecting invisible hydrogen gas emissions.
From outside, astronomers believe it would look like a bright white spiral with soft blue arms.