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L15.docx

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Department
Science
Course
SCI 238
Professor
Mike Fich
Semester
Winter

Description
L15when the supernova explodes it expels heavy elements into space and produces new elements heavier than iron in the ejecta This is the only known process that makes these elementsall are small dense no fusion masses from 1MSun to 10MSun radii constantgravitypressure balancepressure support needed depends on masswhite dwarf WDneutron star NSblack holesequence of mass pressure support limits density radiusWhite Dwarfsthe exposed core of a star that has died and shed its outer layers in a planetary nebula It is quite hot when it first forms because it was the inside of a star but it slowly cools with time no internal energy sourcewhite dwarfs coolblack dwarf o Its size will never change because its electron degeneracy pressure will forever keep it stable against the crush of gravityif they were gaseous they would contract as the gas pressure would decreasebut white dwarfs are supported by electron degeneracy pressureP not dependent on temperature depends only on density and number eof electrons o this has an interesting and important effect on the stars structure the more massive the star is the smaller it is o masses like those of stars o sizes radii like that of Earth o can shine quite brightly in highenergy light such as ultraviolet and X rays o starlike mass and a small size makes gravity very strong near its surface o leads to an upper mass limit for white dwarfs must be less than 14 Solar Masses What happens to more massive dead stars o electron speeds are higher in more massive white dwarfs o electron speeds would reach the speed of light in a white dwarf with a mass of about 14 times the mass of the Sun 14MSun o the pressure that opposes gravity must come from some other source The source is degeneracy pressurethe same type of pressure that supports the failed stars that we call brown dwarfs and that arises when subatomic particles are packed as closely as the laws of quantum mechanics allow o electron degeneracy pressure closely packed electrons
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