Berkeley ASTRON 10 - The Death of Stars (17 pages)

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The Death of Stars



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The Death of Stars

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Lecture Notes


Pages:
17
School:
University of California, Berkeley
Course:
Astron 10 - Introduction to General Astronomy
Introduction to General Astronomy Documents

Unformatted text preview:

The Death of Stars Today s Lecture Post main sequence Chapter 13 pages 296 323 How stars explode supernovae White dwarfs Neutron stars White dwarfs Roughly the size of the Earth with the mass of the Sun If you try to pack electrons into the same place they must be at different energy levels like the energy levels of an atom Each electron must be at a higher energy than the one before it All these energetic electrons in one place give rise to a pressure ELECTRON DEGENERACY PRESSURE This is weird stuff one teaspoon of white dwarf weighs 3 tons If a white dwarf is more massive it actually has a smaller radius No nuclear reactions are taking place the white dwarf just radiates its heat and continues to cool over time White dwarfs are sometimes used as age indicators in globular clusters Types of White Dwarfs The Sun will become a carbon oxygen white dwarf with a mass of 0 6Msun Stars up to 8Msun become carbon oxygen white dwarfs with masses up to 1 1Msun Stars below 0 45Msun aren t massive enough to burn helium in their core and become helium white dwarfs Stars with masses from 8 10Msun have an extra stage of burning in their core and make oxygen neon magnesium white dwarfs with masses of 1 2Msun White dwarfs have a mass limit 1 4Msun the Chandrasekhar limit above which electron degeneracy pressure can t hold up the star Mass exchange in binaries Single stars evolve in a simple manner Lifetime on the main sequence mostly depends on mass Most stars are in binary systems allowing exciting things to occur mass exchange Once material passes this point it flows onto the white dwarf Cataclysmic Variables If one star is a white dwarf and the other star fills its Roche lobe like a growing red giant material can accrete onto the white dwarf Red Giant Angular momentum prevents material from directly hitting the white dwarf forming an accretion disk Accretion disk Cataclysmic variables are bright source in the blue and ultraviolet White dwarf Novae this is the plural Cataclysmic



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