13-Stars - Stellar Evolution and the Origin of the Elements...

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Stellar Evolution and the Origin of the Elements Biology 190A Lecture 13 ‐‐‐ Prof. Steve Schneider Dept. of Astronomy
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t 8,000,000,000 years Solar System Forms • Star formation is like galaxy formation in miniature. ost gas is pulled to center but rotation f the • Most gas is pulled to center, but rotation of the cloud makes leaves some material in a flat disk.
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The Star–Gas–Star Cycle Hot gas cools, forming denser ouds of mostly hydrogen clouds of mostly hydrogen. Dust particles condense and ield interior from ht — shield interior from light cloud cools further. ergy gradually radiated away over millions of Energy is gradually radiated away over millions of years allowing the cloud to contract. terior heats up; s rs form, live, die and expel Interior heats up; stars form, live, die and expel heavy elements back into interstellar space. ter generations of stars have more of the heavy Later generations of stars have more of the heavy elements available when they form.
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A Forest of Stars From their outward appearance, we can etermine two major roperties of stars: determine two major determine two major properties of stars: properties of stars: ± Luminosity Luminosity (from brightness (from brightness and and distance) distance) ± Temperature Temperature (from color: blue=hot, red=cool) (from color: blue=hot, red=cool) Astronomers classify these stars from hot to cold: “O B A F G K M” and recently added o ven cooler classes: & two even cooler classes: L & T The Sun is a G type star .
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Star Birth The cold cloud of gas exerts a gravitational pull on its outer parts, causing the cloud to contract. Bigger “clumps” within the cloud collapse faster, forming massive stars. When these stars begin to shine, the surrounding gas is heated and glows
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The Orion Nebula: Star rming Region A Star Forming Region NASA/CXC/Penn State/E.Feigelson & K.Getman et al., NASA/STScI/Rice Univ./C.O’Dell et al., ESO/VLT/M.McCaughrean et al.
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A Star Is Born! A collapsing cloud of gas grows steadily otter until nuclear fusion of hydrogen to hotter until nuclear fusion of hydrogen to helium begins in its interior (at around 000 000 degrees) 5,000,000 degrees). The release of nuclear energy halts the ll d th t t bili collapse and the star stabilizes. At this time it becomes a “ Main Sequence star fusing H into He in its core.
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Hydrogen Fusion Above about 5,000,000K protons (hydrogen nuclei) slam into each other through a sequence of steps and FUSE into helium.
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This note was uploaded on 11/22/2011 for the course BIOLOGY 190a taught by Professor Staff during the Fall '11 term at UMass (Amherst).

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13-Stars - Stellar Evolution and the Origin of the Elements...

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