Life Cycles of Stars
The Hertzsprung-Russell Diagram
How Stars
Form
• Collapsing gas
and dust cloud
• Protostar mostly infrared
Main Sequence Stars
• Brown Dwarf
• Red Dwarf
• Normal Star
All Objects Exist Because of a
Balance Between Gravity and
Some Other Force
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People, Planets-Interatomic Forces
Normal Stars-Radiation
White Dwarfs-Electron Repulsion
Neutron Stars-Nuclear Forces
Black Holes-No Known Force
How Stars Die
• Main Sequence Stars Brighten With Age
• The More Massive a Star, the Faster it Uses
Fuel
• Giant Phase
• White Dwarf
• Supernova
– Neutron Star - Pulsar
– Black Hole
Historical Supernovae
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1006 - Chinese
1054 - Chinese, European, Anasazi?
1572 - Tycho’s Star
1604 - Kepler’s Star
1987 - Small Magellanic Cloud
(170,000 l.y.)
Life (Briefly!) Near a Supernova
• Sun’s Energy Output = 77 billion
megatons/second
• Let’s relate that to human scales. What
would that be at one kilometer distance?
• 77 x 1015 tons/(150 x 106km)2 = 3 tons
• Picture a truckload of explosives a km away
giving off a one-second burst of heat and
light to rival the Sun
Now Assume the Sun Goes
Supernova
• Brightens by 100 billion times
• Our 3 tons of explosive becomes 300,000
megatons
• Equivalent to entire Earth’s nuclear arsenal
going off one km away - every second
• This energy output would last for days
Planetary Systems
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Protoplanetary Disks
Accretion of Planets
Expulsion and Migration of Planets
About 30 extrasolar planets known
Our Solar System may be unusual?
Protoplanetary Disks in Orion