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Lecture

NATS 1740 Lecture Notes - Electron Degeneracy Pressure, White Dwarf, Degenerate Matter


Department
Natural Science
Course Code
NATS 1740
Professor
Randy Hoffman

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Chapter 13 The Bizarre Stellar Graveyard
13.1 White Dwarfs
What is a White Dwarf?
White Dwarf: exposed core of a star that has died and shed its outer layers
quite hot when forms
slowly cools with time
have masses of stars but radii of earth (very dim)
support by electron degeneracy pressure (packed electrons push outward)
White Dwarf Composition, Density and Size
- A teaspoon of white dwarf matter would weigh several tons
- White dwarf formed by stars like our son would leave behind carbon
- Low mass stars form white dwarfs with helium
- More massive white dwarfs are smaller in size
The White Dwarf Limit (Chandrasekhar Limit)
- No white dwarf can have mass greater than 1.4M sun
What can happen to a white dwarf in a close binary system?
- Can slowly gain mass
- In a close binary system, gas from a companion star can spill toward a white dwarf
forming an accretion disk (new energy source) around it
Novae
- a nova is caused by hydrogen fusion on the surface of a white dwarf in a binary star
system
- 100,000 times as bright as sun, shines for a few weeks, not as bright as a supernova
White dwarf super novae
- when it reaches 1.4M of the sun carbon is ignited and star explodes
- massive star supernova occurs when massive star explodes
- light of white dwarf supernova fade steadily
- if a white dwarf gains enough matter to exceed the 1.4 solar mass white dwarf limit, it
will explode in a super nova
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