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Lecture

White Dwarfs

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Department
Astronomy
Course
Astronomy 1021
Professor
Chris Racknor
Semester
Winter

Description
White Dwarfs White Dwarfs are leftover cores of low intermediate mass stars Their composition is Helium for the lowest mass white dwarfs primarily carbon for Sun like stars and carbonoxygen for intermediate mass stars Resist gravity through degeneracy pressure in this case electron degeneracy electrons are as closely packed as allowed Size and Densities Typical WD mass 1 MTypical WD size size of the Earth sunHigh density because one teaspoon of WD material would weigh as much as a small truck More massive WDs are actually smaller and denser then less massive ones More massstronger gravitycontractioncompress matter to higher densityhigher degeneracy pressure for equilibriumWhite Dwarf Limit Higher mass results in higher electron degeneracy pressure which in turn means higher speed of electrons The maximum electron speed is the speed of light The conclusion is that there is a limit to how massive a white dwarf can become and this limit is about 14M and is called the Chandrasekhar limit sunWhite Dwarfs in Binary Systems An isolated white dwarf left by itself will simply cool down but interesting things can happen when they are in a binary system like accretion disksAccretion Disks The white dwarf pulls matter from its companion Conservation of angular momentum causes the spinning disk around the white dwarf and this is the accretion disk Inner particles move much faster than outer particles Keplers laws which causes friction and this heats up
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