Milky Way

Our Home Galaxy

The Akasha Ganga.

The Milky Way is a massive barred spiral galaxy containing billions of stars, gas, and dust held together by gravity. On a dark night, it appears as a faint milky band across the sky.
Image 1

Key Points

  1. Indian name: Akasha Ganga (meaning the celestial river of light).
  2. Spans 100,000 light-years across with 100 to 400 billion stars.
  3. Our Solar System lies inside the Orion spiral arm.
  4. Andromeda is the closest large spiral galaxy to the Milky Way.

Olympiad Fact

It takes our Solar System about 230 million years (one 'Galactic Year') to complete a single orbit around the center of the Milky Way!

The Galactic Center

The Heart of the Spiral.

At the very center of the Milky Way lies a glowing bulge of stars surrounding a supermassive black hole. The entire galaxy, including our Solar System, orbits around this central point.
Image 1

Key Points

  1. Houses a supermassive black hole named Sagittarius A*.
  2. The most crowded region of stars in our entire galaxy.
  3. Located 26,000 light-years away toward Sagittarius.
  4. Thick space dust hides the center from regular telescopes.

Olympiad Fact

The supermassive black hole Sagittarius A* has a mass about 4 million times that of our Sun.

Dark Matter Halo

The Invisible Glue.

The Milky Way is surrounded by a vast, invisible sphere of 'dark matter'. It makes up nearly 90% of the galaxy's mass and provides the extra gravity needed to hold fast-moving stars together.
Image 1

Key Points

  1. Invisible to telescopes because it emits no light or heat.
  2. Acts as gravitational glue holding spinning stars together.
  3. Forms a giant sphere extending far beyond the spiral arms.
  4. Detected only by its gravitational pull on visible stars.

Olympiad Fact

Dark matter is called 'dark' because it does not interact with electromagnetic radiation (light) at all.

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