The formation of stars
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The Formation of Stars. Chapter 11. Giant Molecular Clouds Large Low density Cold. To Form Stars Small High density Hot. 4 Factors that Resist Contraction. Thermal Energy Interstellar Magnetic Field Rotation Turbulence. Shockwaves. Caused by: Supernova Explosions

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Giant Molecular Clouds

  • Large

  • Low density

  • Cold

To Form Stars

  • Small

  • High density

  • Hot


4 factors that resist contraction
4 Factors that Resist Contraction

  • Thermal Energy

  • Interstellar Magnetic Field

  • Rotation

  • Turbulence


Shockwaves
Shockwaves

Caused by:

  • Supernova Explosions

  • Ignition of very hot stars—can ionize nearby gas

  • Collisions of molecular clouds

  • Spiral Pattern of the Milky Way Galaxy


How to get hot enough
How to get hot enough?

Free-Fall Contraction

  • The cloud begins to contract as gravity pulls atoms to the center.

  • Increase in velocity = heating of gas

  • Increase in velocity leads to thermal energy


Protostar
Protostar

  • Definition: A prestellar object that is hot enough to radiate infrared radiation but not hot enough to generate energy by nuclear fusion.

  • Hidden by Cocoons

  • Emit infrared radiation

  • Located on the Birth line of the HR Diagram

  • 0.1% of star’s lifetime


The cno cycle
The CNO Cycle

  • The Hydrogen fusion process that used Carbon, Nitrogen, and Oxygen as stepping stones.

  • Used by main sequence stars with mass greater than 1.1 solar masses

  • Temperatures greater than 16 million K


  • Carbon-12 nucleus absorbs a proton

  • Becomes nitrogen-13

  • Decays into Carbon-13, absorbs a 2nd proton

  • Becomes Nitrogen-14, absorbs a 3rd proton

  • Becomes Oxygen-15

  • Decays into Nitrogen-15, absorbs a 4th proton, ejects a He nucleus

  • Becomes Carbon-12


Energy transport
Energy Transport

  • Conduction

  • Radiation

  • Convection


Inside stars
Inside Stars

  • Upper Main Sequence Stars

    • More massive

    • CNO Cycle

    • Convective Zone in center

  • Lower Main Sequence Stars

    • Least massive

    • Proton-Proton Chain

    • Radiative Zone in center


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