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Nucleosynthesis UPSC NOTE


  • Stellar nucleosynthesis is the process by which stars forge elements inside their cores.

  • The only element not formed in this way is hydrogen, the most abundant and lightest element in the universe: it was formed in the initial aftermath of the Big Bang.

  • The cores of stars have crushing pressures and temperature

  • For example, the sun’s core temperature is about 15 million degrees C. 

  • In these harsh conditions, the nuclei of atoms undergo nuclear fusion.

  • The hydrogen nucleus is just one proton

  • Inside the core, these nuclei come together to form helium nuclei (two protons and two neutrons). 

  • This is the p-p (short for proton-proton) process.

  • In more massive stars, however, stellar nucleosynthesis treads a different path — one dictated by the availability of energy. 

  • More massive stars have a higher core temperature

  • There, in the so-called carbon-nitrogen-oxygen (CNO) cycle, the nuclei of these elements come together in different ways to form elements from helium onwards.

  • When a star runs out of nuclei to fuse, its core contracts

  • This in return increases its temperature, triggering nuclear fusion yet again. 

  • This process goes back and forth until the star starts to produce iron in its core. 

  • Iron is the lightest element for which fusion consumes more energy than it releases

  • Elements heavier than iron can only be synthesised outside a star when it goes supernova.



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Learnerz IAS | Concept oriented UPSC Classes in Malayalam: Nucleosynthesis UPSC NOTE
Nucleosynthesis UPSC NOTE
Learnerz IAS | Concept oriented UPSC Classes in Malayalam
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