Transcript April 10th
Survey of the Universe Tom Burbine [email protected] • If you are unhappy with any of your grades: • You can write a 10 page paper on an astronomical subject to replace it • 12 point font • Times New Roman font • Double space • No figures or plots • Due by May 1st White Dwarf • Sun will end its life as a white dwarf • Stellar Wind – Gas flowing from the star • Carbon and silicon atoms form grains, which are pushed outward by radiation • Red Giant loses material (as much as 10-4 solar masses per year) Planetary Nebula • Expanding glowing shell of ionized gas from a dying star • Hot core ionizes the escaping atmosphere • Colors come from a mix of emission lines such as oxygen (green), nitrogen (red), and hydrogen (pink) White Dwarf • Hot core at the center of a planetary nebula becomes a white dwarf • Very hot • Very small White Dwarfs • Most white dwarfs are composed of carbon and oxygen • Some white dwarfs have the same mass as the Sun but slightly bigger than the Earth • 200,000 times as dense as the Earth • Very dense – Some have densities of 3 million grams per cubic centimeter – A teaspoon of a white dwarf would weigh as much as an elephant Mass transfer • A White Dwarf can accrete matter from a companion star when it is in a binary star system • Hydrogen that is transferred can fuse on the surface of the white dwarf • Explosion can occur, which is called a Nova Nova Explosion • Taken 7 ½ months apart using Hubble Space Telescope • Show a shell of gas expanding away from a white dwarf White Dwarf White Dwarfs • The collapse due to gravity is stopped by electron degeneracy pressure Electron Degeneracy Pressure • No two electrons can occupy the same quantum state So What Does This Mean • Electron Degeneracy Pressure balances the gravitational force due to gravity in white dwarfs One Interesting Thing • More massive white dwarfs are smaller White Dwarf Limit • The mass of a White Dwarf can not exceed approximately 1.4 Solar Masses • Called the Chandrasekhar Limit Exceed Chandrasekhar Limit • When you exceed the Chandrasekhar Limit, the white dwarf collapses • Carbon and Oxygen in the white dwarf reach a temperature where they undergo fusion to silicon 12C + 16O → 28Si • Silicon then fuses to form nickel 28Si + 28Si → 56Ni • White Dwarf explodes and becomes Type Ia supernova Any Questions?