CC105FinalNotes - Stars:BirthtoMiddleAge 06/11/200813:58:00...

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Stars: Birth to Middle Age 06/11/2008 13:58:00 Birth of Stars They are born in clouds. o Dense o Cold The dark clouds obscure our view at visible wavlengths. Radiowaves and and  other types of waves penetrate these dark clouds. Clouds are molecular: mostly hydrogen, but also CO,OH Water, HCN o They can be stdied with molecular things. Star Formation Four Stages 1) Cloud Collapses The stable cloud has a balance of 2 forces Inward and outward force. “Jeans Mass” shoed that the gravity becomes stronger than pressure  when the mass get large enough if clouds (or fragments of clouds) acquire enough mass,  the cloud will collapse . 2) Protostar forms Collapase to Protostar The center of a collapsing cloud becomes denser and  darmer.
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3) Disk forms Conservation Law: The following quantities are conserved: Energy Momentum Angular momentum- the tendency of an object that is  spining to stay spinning. L = mvr L=angular momentum M=mass V=velocity R=radius o If the radius decreases, and angular  momentum is conserved, the velocity must  increase. The total amount of these quantities never changes . 4) Planets form A star is born Then the central protostar becomes hot and dense enough, it becomes a star  and generates its own energy. The sun must be a fluid! It is composed of hydrogen and helium gas.
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Stars Archimedes Law o An object will float if it is less dense than the medium o An object will sink if it is denser than the medium. Convection: A cycle of floating and sinking. o Object heats, expands, grows less dense, and floats. Stellar structure: governed by hydrostatic equilibrium o At each point, gravity inward balances pressure outward o More weight toward center means that the density and temperature  increase as the radius decreases. Energy Gernation Important fact: o The age of our solar system is about 5 billion years. Only nuclear  energy can keep the sun shining this long. Nuclear Fusion o Convert mass-energy of nucleus into starlight o Convert 4 hydrogen   helium o Begning mass 4 m H o Ending mass: m He These conditions confine nuclei, and slam them together at high speeds The result is nuclear fusion. The Sun The sun is 1 of a billion stars in the universe. How does is compare to other  stars.
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The Death of Stars 06/11/2008 13:58:00 Synthesis of Elements
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The early Universe contained no elements heavier than helium Where do the heavier elements come from? The main sequence star mainly “burns” hydrogen into helium via nuclear 
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CC105FinalNotes - Stars:BirthtoMiddleAge 06/11/200813:58:00...

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