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

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Stellar Evolution and the Origin of the Elements Bi l 190A 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. • Most gas is pulled to center but rotation of 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 clouds of mostly hydrogen clouds of mostly hydrogen. Dust particles condense and shield interior from light — shield interior from light cloud cools further. Energy is gradually radiated away over millions of years allowing the cloud to contract. Interior heats up; stars form, live, die and expel heavy elements back into interstellar space. 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 determine two major determine two major properties of stars: properties of stars: Luminosity Luminosity (from brightness (from brightness and and distance) distance) (f l bl h d l) 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 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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