In the previous sessions we discussed about gravity and its applications in this session we need to discuss about the stellar energy......!
How stars get energy to illuminate the energy?
how they are emitting heat and light  from thousands and millions of years together?
lets have a detailed history about this concept.... 

 This observations and researches were started in mid 1800's.......
In the mid 1800;s two physicists lord kelvin and Hermann von helmholtz,put forward the idea that the huge weights of sun's outer layers should cause the sun to gradually contract.as it does  so the gases in its interior becomes compressed and when a gas is compressed its temperature increases...and these two scientists argued that gravitational contraction would cause the suns gases to become hot enough to radiate heat energy into space.This process called kelvin-Helmholtz contraction,does infact happen in the protostar phase of stellar formation.....

But after them in 1920 Aurthur Eddington proposed that stars obtain their energy from nuclear fusion of hydrogen to form helium and raised the possibility that the heavier elements are produced in stars.this was the preliminary step towards the idea of nucleosynthesis in 1928.....

And in 1939,hans bethe analyzed different possibilities of analyzed the different possibilities for reactions by which hydrogen is fused into helium. He defined two processes that he believed to be the sources of energy in stars.they are1.proton-proton chain reaction  and 
2.carbon-nitrogen cycle.which are the two main energy sources for the stars..



1.proton proton cycle:
 this cycle consist of three steps in which hydrogen is converted to helium

And the next proecss is carbon-nitrogen cycle(or)cno cycle:                                                                                  

 

  

    

 

In the way the two processes continues till the all available atoms completely gets converted to Helium or the energy (heat and light or even radiation )                                                                                                                                                                                                                             

 

 .And we may have to consider the newly emerged theories by which stellar energy is produce are given as follows...................                                                                                            

                     The most important reactions in stellar nucleosynthesis:

•  Hydrogen fusing:
  • Deuterium burning
  • The proton-proton chain
  • The carbon-nitrogen-oxygen cycle
• Helium burning:
  • The triple-alpha process
  • The alpha process
• Burning of heavier elements:
  • Lithium burning: a process found most commonly in brown dwarfs
  • Carbon burning process
  • Neon burning process
  • Oxygen burning process
  • Silicon burning process
• Production of elements heavier than iron:
  • Neutron capture:
    • The R-process
    • The S-process
  • Proton capture:
    • The Rp-process
  • Photo-disintegration:
    • The P-process