The Milky Way Galaxy is a large barred spiral galaxy with a complex structure consisting of a central bulge, spiral arms, and a surrounding halo. It contains our Solar System and is part of the Local Group of galaxies with hundreds of billions of stars, along with interstellar gas, dust, and dark matter. The Milky Way plays a central role in our understanding of galactic dynamics and structure. Its study provides valuable insights into the formation and evolution of galaxies throughout the universe.

1. 1. Structure and components

• • • Spiral Shape: The Milky Way is a barred spiral galaxy with a central bar-shaped structure and spiral arms extending from it.
    • Galactic Core (Bulge): A dense, spherical region at the centre of the galaxy, containing older stars and a likely supermassive black hole known as Sagittarius A.
    • Galactic Disk: A flattened, rotating disk where most of the galaxy’s stars, gas, and dust are located. This includes the prominent spiral arms.
    • Spiral Arms: Four main arms are Perseus, Carina-Sagittarius, Scutum-Centaurus and Orion, extend from the central bar and are sites of active star formation.
    • Galactic Halo: A spherical region surrounding the disk, containing older stars, globular clusters, and dark matter.

 

1. 2. Size and Composition

• • • Diameter: Approximately 100,000 to 120,000 light-years.
    • Thickness: About 1,000 light-years thick in the disk.
    • Number of Stars: Estimated to contain between 100 billion and 400 billion stars.
    • Interstellar Medium: Contains a mix of hydrogen, helium, and dust, which plays a crucial role in star formation.

 

1. 3. Location and Motion

• • • Location: The Milky Way is situated in the Local Group of galaxies, which includes the Andromeda Galaxy, the Triangulum Galaxy, and several smaller galaxies.
    • Motion: The Milky Way is rotating with a velocity of about 828,000 km/h (514,000 mph) relative to the Cosmic Microwave Background (CMB). It orbits around the centre of mass of the Local Group.

 

1. 4. Observational Features

• • • Visible Light: From Earth, the Milky Way appears as a bright band stretching across the night sky, especially visible from locations with minimal light pollution.
    • Star Clusters and Nebulae: Prominent features include the Orion Nebula, the Pleiades star cluster, and the Hercules Globular Cluster.

 

1. 5. Galactic Dynamics

• • • Supermassive Black Hole: The core of the Milky Way harbours a supermassive black hole with a mass of about 4 million times that of the Sun.
    • Dark Matter: The galaxy’s rotation curve suggests the presence of dark matter, an invisible form of matter that influences its gravitational dynamics.