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 1.Thermal Energy 2.Interstellar Magnetic Field 3.Rotation 4.Turbulence

Shockwaves Caused by: 1.Supernova Explosions 2.Ignition of very hot stars—can ionize nearby gas 3.Collisions of molecular clouds 4.Spiral Pattern of the Milky Way Galaxy

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 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 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 2 nd proton Becomes Nitrogen-14, absorbs a 3 rd proton Becomes Oxygen-15 Decays into Nitrogen-15, absorbs a 4 th proton, ejects a He nucleus Becomes Carbon-12

Energy Transport 1.Conduction 2.Radiation 3.Convection

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