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Published byJustin Nelson Modified over 9 years ago
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Stars
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Life cycle of star http://www.youtube.com/watch?v= H8Jz6FU5D1A http://www.youtube.com/watch?v= H8Jz6FU5D1A
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http://aspire.cosmic- ray.org/labs/star_life/starlife_proto. html
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1. Nebula = cold, dark cloud of dust and gas [mostly H]
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gravity pulls particles, to clump together
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Accretion: accumulating more mass
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Clumps increase in size [accretion] pressure and temperature increases [due to KE of particles]
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2. Protostar when forces are in equilibrium : gravity collapses particles together, high temperature/pressure pushes particles apart. At equilibrium Gas pressure = gravity
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If protostar too small, becomes brown dwarf, never a real star.
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4. STAR If enough mass, critical temperature protostar core begins to fuse H into He : star is born.
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The star is stable while the gravitation pulling the star together is balanced by the internal pressure pushing it apart.
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During lifetime, stars fuse Hydrogen into Helium and then fuse helium into Carbon.
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Massive stars can fuse carbon into heavier elements.
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3. Main sequence
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90% of stars spend majority of life on the Main Sequence
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On the main sequence, hydrogen is fused into helium H is fused into He..
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Main sequence is a grouping of stars by size, color, luminosity
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We compare other stars to the brightness [luminosity ] of the Sun:
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Temperature determines the color of a star TemperatureColor 30,000 - 60,000 KBlue stars 10,000 - 30,000 KBlue-white stars 7,500 - 10,000 KWhite stars 6,000 - 7,500 KYellow-white stars 5,000 - 6,000 KYellow stars (like the Sun) 3,500 - 5,000KYellow-orange stars < 3,500 KRed stars
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Mass-luminosity relationship for Main Sequence Stars L = L o [M/M o ] 3.5 Lo = luminosity of Sun Mo = mass of Sun
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The Herzsprung-Russell Diagram H-R diagram shows relationship of luminosity, temperature, size
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[ H-R diagram]
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Note the scales are log scales, not linear.
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Mo is the mass of the Sun Low mass stars: 0.5Mo medium mass stars: 0.5Mo – 3Mo massive stars: >3 Mo
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Larger, hotter stars burn out very fast - in a few million years. Smaller, cooler stars burn slowly for billions of years
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The Sun is a medium yellow star. The surface temperature is about 6000K The Sun has a life expectancy of about 10 billion years
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Try the interactive star lab: http://aspire.cosmic- ray.org/labs/star_life/starlife_seque nce.html http://aspire.cosmic- ray.org/labs/star_life/starlife_seque nce.html
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Wh
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After becoming red giant low mass stars [mass of Sun] shrink into white dwarfs. Radius is close to radius of Earth.
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Medium mass stars [ 1.4 to 3 Mo] expand into Red Giants, collapse and then explode into a supernova
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Finally becomes a neutron star [about the size of Manhattan]
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Massive stars collapse and begin to fuse carbon. They explode as supernova and the core is crushed into a black hole.
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After all H is fused, star leaves the main sequence.
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Pressure increases, stars expand enormously and cool.
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Small stars expands and sheds outer layers
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Medium stars expand into red giants
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After about 100,000 years the protostar has drawn in enough dust and gas to become a star.
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When core temperature reaches 10 million degrees, H begins to fuse into He, releasing energy [heat]
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Most stars are Main Sequence Stars
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When core H has all fused to He,
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About 1 million Earth’s fit in the Sun
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http://www.youtube.com/watch?v= g4iD-9GSW-0
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Sun compared to largest star
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http://www.youtube.com/watch?v= Bcz4vGvoxQA
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HR diagrams http://www.youtube.com/watch?v= Kqe6F-Qf9Tk http://www.youtube.com/watch?v= Kqe6F-Qf9Tk
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Black hole swallows a star http://www.youtube.com/watch?v= O3Z5AS3TTS4 http://www.youtube.com/watch?v= O3Z5AS3TTS4
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