If you are here, you must be wondering about the Milky Way, Earth's home galaxy. What does it exactly look like? In what part is our Sun located in this vast structure? What is the galaxy composed of?
If these are some of the questions buzzing around your head, you have come to the right place. We are going to look at the basics of the Milky Way. We are going to look at the basics of the Milky Way i.e. its structure and learn a lot about it that we never knew before!
The Classification
We all know that every classification is done on the basis of some features that bifurcate each component very neatly. And for determining the components of the Milky Way, the features responsible were gas, dust, and stars. More specifically, the distribution of gas, dust, and stars.
And on that basis, Milky Way was found to be composed of four main components - thin disk, thick disk, central bulge and the halo.
A closer look at the components
Thin Disk
This part is the thinnest in width (only around 325 pc) but extends in length to about 20 kpc. This is the home to our Sun and is massively populated by gas, dust, and the younger generation of stars. This component is in turn divided into two parts on the basis of the ages of the stars found in them.
Young thin disk: As the name suggests the population of stars in this region is the youngest. This is also the star-forming region of the galaxy and extends up to a height of about 100 pc.
Old thin disk: This part does contain young stars but not the star formation region and extends to up to 325 pc.
Thick disk
The thickness of this disk is ~ 1 kpc. It has a meager contribution (~ 2%) to the total mass density of the galactic plane. In short, even though it is spanning vast space, it is very sparsely populated.
Central Bulge
The central part of the galaxy with a significant-looking bulge is what we very obviously call the central bulge or just the bulge. This part of the galaxy looks redder than any other part and indicates that the stars here are old. And how do we know the stars are old? This is because the older stars are depleting of their fuel and are less hot hence their radiation peaks at the red part of the spectrum.
Halo
This component of the galaxy is almost spherical in shape and houses old stars and globular clusters. Even though it might not look the part, it is definitely a part of the galaxy system and hence made it in the list of its components. The fact is that this region goes beyond the very obviously visible components. The stars (generally old) and the clusters lying in this region are bound to the galactic gravity and surprisingly make a decent ~1% of the galactic mass. And if you are wondering why only old population of stars reside here? That's a good topic for your research.
An interesting fact
It is very evident that out of all the features, the main one that bifurcates these different components of the galaxy is the different types of stars. Do you think it can shed a little light on the evolution of the galaxy? In fact, it does! The presence of different types of stars (depending on age) tells us that the galaxy formed and evolved in different phases. Isn't it wonderful how such a small and easily ignored subject of galaxy structure can shed light on a bigger question about the evolution of our galaxy?
Glossary
pc/kpc: (parsec/kiloparsec) The measure of distance used in astronomy. 1pc = 3.26 lightyears
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