Galactic Star Formation

Prince Khatarkar September 29, 2015

1 FORMATION

Stars are born by gravitational collapse of dense interstellar clouds of gas. Slight density perturbation in Nebula lead to an initially isothermal collapse if the mass is larger than a certain critical mass called Jeans Criterion. Adiabatic process takes over when the free fall time becomes comparable with low temperature, high opacity and thus mostly convective cores. They are located on the Hayashi track in the H-R diagram. Once in hydrostatic equilibrium it is said to have entered the pre main sequence phase. Further contraction increases the internal temperature and lowers the opacity thereby making the convective core recede towards the cen- tre. Radiative contractions with almost unchanged effective temperature and constantly decreasing luminosity ensures that the stars comes down in the H- R diagram and enters the Henyey track. Increasing core temperature initiates Hydrogen burning: Protium to Deuterium and finally to Helium-3. Helium-3 being scarce, the full proton-proton chain cannot be completed and the highly temperature sensitive nuclear reaction forms a convectictive core. Depending upon the masses of there convectictive core star goes into different cycles. After the pre main sequence phase and main sequence phase a star is formed.

2 Star Classification

Those with masses in between 1.6 Solar mass and 9 Solar mass end their ac- cretion phase before main sequence- Herbig Ae/Be stars. Those with masses between 0.8 Solar mass and 1.6 Solar mass light up as optically bright sourses called T Tauri stars.

REFERENCES References

[1] Dina prialnik, “An Introduction to the theory of stellar structure and evo- lution”,2000.

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