ASTROCHEMISTRY- EPISODE 2 (THE AGE OF STARS AND INTERSTELLAR DUST)

Master Obi Wan Kenobi: Welcome, Young Padawan.

Glad to have you back on our journey in astrochemistry. Let’s start today by talking about some stars! When molecular clouds of Hydrogen collapse under their own gravity, they give rise to stars. The energy released in the core of these stars due to the “burning” of these gases gives rise to heavier elements and this process is known as nucleosynthesis. When the stars die, these elements within them may form interstellar gas. Or they may remain in the following phases of the star’s life cycle, that is, as neutron stars, black holes or white dwarfs. So how do you think this helps us?

Anakin: umm… How does this help us?

Obi Wan: I expected nothing less. Well, if you used your brains as much as you used your lightsaber, it would be apparent that this knowledge could help you tell the age of a star!

Anakin: And in which world would I actually want to know that?

Obi Wan: *ignores* The amount of metals in these gases or celestial bodies generally increases with time. So if we can measure the changes in the amount of chemical elements present in the galaxies over time, we might be able to estimate their ages. On average, younger stars should contain more iron than older stars.

Anakin: Hold up! Technically shouldn’t older stars have a greater amount of Iron owing to the additional ~1 billion+ years of accumulation, master?

Obi Wan: Someone is finally listening, are they? Well, supernova events towards the end of a star’s life cycle leads to the layers with heavy metals being blown away. These metals will then associate with hydrogen clouds and develop into newer stars. This means that the relative abundance of the heavy elements must be less and less in older stars.

Anakin: I should stop asking questions, it makes you talk more and quite frankly we need to be concise for the sake of this post.

Obi Wan: And there we go again, you are on a roll today anakin, with all these…

Anakin: Master!

Obi Wan: Alright then, moving on to another fundamental concept in this vast mostly obscure field of astrochemistry: Interstellar Grains.

Interstellar dust grains form in dense, cooler environments (like atmospheres of red giants). They are released from stars by stellar winds, radiation pressure or stellar explosions. They start off as carbon and silicon grains, collect other elements like nitrogen, hydrogen, oxygen to form icy particles and then get surrounded by sticky organic molecules and simple organic compounds(these are formed by interaction of the icy particles with UV light).

Anakin: Are we really going to learn about dust now? The dust that floats around on Tatooine?

Obi Wan: *shakes his head in absolute exasperation* Typical interstellar dust grains are a lot tinier than the dust we see on Tatooine, Anakin. In fact, these are almost as small as the wavelength of blue light!

Anakin: Does that mean that they can absorb and scatter blue light?

Obi Wan: Exactly! Thus the dust cloud happens to appear redder than it should be, known as interstellar reddening. Dust grains have a very important role in the formation of stars, too!

Obi Wan: New stars could never be formed without all these processes occurring within molecular clouds.

Anakin: Great! This will benefit me greatly in the war on Geonosis.

Obi Wan: Tone down the snarkiness will you?

The purpose of The Jedi Order is to maintain peace and harmony in the galaxy Anakin, and that requires us to study The Force that surrounds us in detail.

Anakin: Nerd.

Reference: astronomy.swin.edu.au/cosmos/

Writers: Sahil Lalsodagar, Shailaja Nautiyal