A35 Lectures 14-15 - Lecture 14 Aging and Death for Stars Inverse square law quantity is inversely proportional to the square of the distance

A35 Lectures 14-15 - Lecture 14 Aging and Death for Stars...

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Lecture 14: Aging and Death for Stars * Inverse square law: quantity is inversely proportional to the square of the distance * Hertzsprung-Russell Diagram: luminosity vs. temperature, need flux and parallax to measure luminosity, most stars on main sequence * H-R: for a main sequence star, high mass means high luminosity (luminosity and mass related) * Lifetime depends on the amount of hydrogen in the star’s core and the rate at which the hydrogen is consumed (more massive stars have shorter main sequence lifetimes) * Sun has been main sequence star for about 4.56 billion years, should remain one for another 7 billion years * During main sequence lifetime, a star will expand a little and increase a little in luminosity * As core runs out of hydrogen (H fusion), main sequence star becomes Red Giant (happens most rapidly for high mass, luminous stars) * Earth will melt and evaporate when sun is red giant * Fusion of He into carbon and oxygen begins at center of red giant when temperature hits 100 million K – “triple alpha process” * Clusters: same age, same composition, same distance, “a gang of stars” * Age of star cluster can be determined by plotting its stars on H-R diagram, based on turn-off point * As a cluster ages, the main sequence is “eaten away” from the upper left as stars of
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  • Spring '09
  • RobertKirshner
  • White dwarf, main sequence

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