Nucleosynthesis: The element Factory

Context

Nucleosynthesis is the process of forming atomic nuclei in stars and other cosmic environments. It gives rise to large fractions of the constituents of the universe from the lighter to the heavier. Nucleosynthesis scenario is one of the most useful models for astrophysics and cosmology since it explains how the Universe was formed and what elements we can find here at the present moment.

Big Bang Nucleosynthesis

Big Bang Nucleosynthesis is the first or most explosive phase of nucleosynthesis which occurs during the initial few minutes following Big Bang. This period was still hot and dense with temperatures well above billions of degrees. Therefore, protons, neutrons, electrons and photons together conspired and assembled the smallest elements which referred to hydrogen, helium and lithium. This is a very crucial stage in the development of the Universe in preparation for a later nucleosynthesis of heavier elements.

Stellar Nucleosynthesis

Stellar nucleosynthesis occurs in the stars which happen in the interior parts of the stars at pressures and temperatures that are sufficiently high to support nuclear reactions. There are two main types of stellar nucleosynthesis: Gaseous carbon-nitrogen-oxygen cycle and the triple-alpha process. The CNO cycle occurs in stars of the following sizes: 1. 5 and 2. 5 solar masses in which carbon nitrogen and oxygen are found where fusion takes place. An example of a triple-alpha process is that it occurs in the more massive stars in which the alpha particles (Helium nucleus) is combined with the carbon that is being formed and other elements such as oxygen, silicon and iron.

Supernova Nucleosynthesis

Supernova Nucleosynthesis is related to stellar evolution where stars eventually expire and reach extremely high temperatures and densities to allow for elements that are heavier to form. There are two types of supernovae: Type II Supernovae and Type Ia Supernovae . This could be a Type II supernova that can be observed when the massive star runs out of fuel and starts to collapse, creating a great explosion for the production of heavier elements such as nickel, cobalt and iron. Type Ia supernovae on the other hand produce elements such as iron; nickel and chromium because a white dwarf star that forms this supernovae reaches a critical mass and explodes in a thermonuclear explosion due to it accreting material from its companion star.

Neutron Capture Nucleosynthesis

Neutron Capture Nucleosynthesis occurs when atoms add more of the neutrons and therefore result in the formation of heavier elements. This process occurs in two main environments: Post aspirational phase AGB stars models and neutron star mergers. AGB stars are low mass stars in later stages of stellar evolution when helium flashes are utilised for the generation of other elements like carbon nitrogen oxygen. On the other hand we have a case of neutron stars that are as catastrophic as the case since here we have got two neutron stars hitting and giving rise to heavy elements like gold uranium and plutonium.

Cosmic Ray Nucleosynthesis

Cosmic Ray Nucleosynthesis is a theory that explains the production of newly formed elements created as a consequence of an interaction with an atomic nucleus through high-energy particles known as cosmic rays. This is the process that creates the light elements that include lithium, beryllium, and boron. These elements are produced when the rays from the atmosphere known as the cosmic rays interact with molecules in the atmosphere thus producing streams of particles known as the elements.

Nucleosynthesis in the Universe

Nucleosynthesis is a very important process when regarding the evolution of the universe. All the elements that exist in the universe have been formed through nucleosynthesis from the lightest elements that were formed in the big bang to the hardest elements that are formed through the neutron star’s collision. The periodic table also represents the elements in the universe through their ability to form in large quantities through nucleosynthesis and similar processes that lead to the enhancement of the abundance of certain elements in the universe. In order to understand the formation of the elements these days, there has to be an understanding of the process of nucleosynthesis.

Conclusion

Nucleosynthesis remains an interesting and engaging phenomenon that defines the nature of the universe as it exists today. Over 13.8 billion years from the big bang up to the current date, all the elements found in the universe from the lightweight to the heavyweight have been synthesised through the process of nucleosynthesis.

Source: The Hindu

UPSC Prelims Practice Question

Which of the following statements about nucleosynthesis is/are correct?

1. Nucleosynthesis is the process by which new atomic nuclei are created from pre-existing nucleons (protons and neutrons).
2. The Big Bang nucleosynthesis primarily produced heavy elements such as iron and uranium.
3. Stellar nucleosynthesis occurs in the cores of stars and is responsible for the creation of elements heavier than hydrogen and helium.
4. Supernova nucleosynthesis contributes to the formation of elements heavier than iron.

Select the correct answer using the codes given below:

a) 1 and 3 only
b) 2 and 4 only
c) 1, 3, and 4 only
d) 1, 2, 3, and 4

Ans- c

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