The Milky Way: Exploring Our Grand Cosmic Neighborhood

 

        Our universe is filled with countless mysteries, and our own cosmic address is 'Mandakini' (The Milky Way). From a scientific perspective, the Milky Way is not just a cluster of stars, but an extremely complex, living, and dynamic system.

1. Structure and Dimensions

        The Milky Way consists of approximately 100 Billion stars and vast Nebulae. To an observer in space, it appears as a 'Spiral' galaxy.

• Shape: Viewed from the top, it looks like a rotating wheel (disk), but from the side, it resembles a flattened disc or a puffed-up 'puri'.
• Diameter: Approximately 100,000 Light-years.
• Central Bulge: The thickness of the Milky Way’s center is about 15,000 light-years, where the density of stars is highest.
• Sun's Location: Our Sun is an average star located in the 'Orion Arm', about 30,000 light-years away from the center. At the Sun's position, the galaxy is about 2,500 light-years thick.

2. Spiral Arms and Star Formation

        The most striking feature of the Milky Way is its Spiral Arms. These arms are actually dense bands of gas and dust wrapped around the center.

• Star Nursery: These arms contain extremely hot blue stars and clouds of Ionized Hydrogen. Due to gravity, these gas clouds collapse, giving birth to new stars.
• Major Arms: Our galaxy has major arms like Sagittarius, Perseus, Cygnus, and Orion. These arms are typically 10,000 light-years long and 500 light-years wide.

3. Galactic Rotation and Dynamics

        The Milky Way is not stationary in space; it is constantly rotating on its axis. This motion is not like a 'Solid Body' but varies according to the distance from the center.

• Orbital Speed: At the Sun's location, it orbits the center at a speed of approximately 210 km/s.
• Cosmic Year: It takes the Sun about 220 to 250 million years (22 to 25 crore years) to complete one orbit around the galactic center. This period is known as a 'Cosmic Year'. Since its birth, the Sun has completed about 30 such orbits.
• Changing Constellations: Due to this rotation, the relative positions of stars change over millions of years. Because of this, constellations like Ursa Major (Saptarshi) looked different thousands of years ago and will change again in the future.

4. Stellar Populations

        Scientists have classified stars into two main categories based on their age and chemical composition:

• Population I: These are young stars, rich in 'metal' elements. They are primarily found in the Spiral Arms. Our Sun belongs to this category.
• Population II: These are ancient, older stars. They are found in the Central Bulge and the surrounding Galactic Halo. Stars in the halo do not participate in the galaxy's rotation.

5. The Galactic Center and Black Hole

        According to modern research, a powerful Supermassive Black Hole exists at the center of the Milky Way, known as 'Sagittarius A' (Sgr A)**.

 Conclusion

        The Milky Way is not just a collection of stars but a vast and wonderful system. It continuously produces new stars and contributes to the evolution of the universe. As science advances, Radio Telescopes are providing us with clearer information about this magnificent stellar world.