Download 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?