Astro 18.1 White dwarfs Sun leave white dwarf when dead High mass leave neutron star or black whole White dwarf is exposed core of star Quite hot at first Slowly cools Stellar in mass small in size Very strong gravity Degeneracy pressure keeps it alive ? in this case from electrons White dwarf composition Sun size star left over = mostly carbon Small star = mostly helium Larger sized = large amts of oxygen or even heavier More massive white dwarfs are smaller in size than less massive White dwarf limit ? 1.4 M of sun because electron can?t go past speed of light White dwarf cool -> black dwarf White dwarf in close binary system can gain mass if companion is a main sequence or giant star Accretion disk Novae When fusion starts in the accretion disk of white dwarfs. Shines for few weeks Far less luminous than supernova Can shine like 100000 Suns White dwarf supernova ? sudden carbon fusion ignites in it Peak L of about 10 billion times the sun Fades quickly during first few weeks Lack of H lines
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