1. Survey of the Universe Tom Burbine tburbine@mtholyoke.edu

2. 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

3. White Dwarf Sun will end its life as a white dwarf

6. 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)

7. 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)

9. White Dwarf Hot core at the center of a planetary nebula becomes a white dwarf Very hot Very small

10. 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

11. Mass transfer A White Dwarf can accrete matter from a companion star when it is in a binary star system

13. Hydrogen that is transferred can fuse on the surface of the white dwarf Explosion can occur, which is called a Nova

14. Nova Explosion Taken 7 ½ months apart using Hubble Space Telescope Show a shell of gas expanding away from a white dwarf

15. White Dwarf

16. White Dwarfs The collapse due to gravity is stopped by electron degeneracy pressure

17. Electron Degeneracy Pressure No two electrons can occupy the same quantum state

18. So What Does This Mean Electron Degeneracy Pressure balances the gravitational force due to gravity in white dwarfs

19. One Interesting Thing More massive white dwarfs are smaller

20. White Dwarf Limit The mass of a White Dwarf can not exceed approximately 1.4 Solar Masses Called the Chandrasekhar Limit

21. 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 12 C + 16 O → 28 Si Silicon then fuses to form nickel 28 Si + 28 Si → 56 Ni White Dwarf explodes and becomes Type Ia supernova

23. Any Questions?