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Transcript
ASTR 1200
Announcements
Observing Opportunity Tonight!!
Best opportunity. Only two more chances.
Last two WILL be colder.
Exams will be returned on Thursday
Problem Sets 3 and 4 posted. Due next week.
Thursday will review equations of light and do Doppler
Shift. (Necessary for PS3)
Second exam will be October 28 and will cover stellar evolution
and endpoints.
Website
http://casa.colorado.edu/~wcash/APS1200/APS1200.html
He Compressed In Middle
H
H->He
He
Temperature and Density
Rise in Center
Star gets more luminous
Electron Degeneracy
•Helium Density Rises
•Center of Sun has density of 10g/cc (H2O = 1g/cc)
•When density in center of star reaches ~30,000g/cc
•a new phenomenon kicks in
•Electron Degeneracy
•A purely quantum mechanical phenomenon
He Flash
Star changes L and R
in just 10,000 years!
After the Flash
H
H
H->He
H->He
He->C
He->C
C
Helium Burns in the Center
Starts to Development Dead C Core
Red Giants
Earth Orbit
Nucleus
Red Supergiant
H
H->He
He->C
C
Meanwhile, down in the core,
the C is becoming degenerate.
Luminosity is becoming so great it
blows the H envelope into space.
Planetary Nebulae
Gas blown out into space and
illuminated by central star.
The star is the degenerate C core.
The Ring Nebula
Hourglass 2
Next Explosion is
Constrained and Expands
as Hour-Glass
What’s Left?
Eventually all the envelope is blown away.
The planetary nebula dissipates.
All we have is the hot, degenerate core.
Settles down to become a White Dwarf
Globular Clusters
Very Old. G stars becoming giants.
All the same age and composition
Can actually see evolution off the MS
White Dwarfs
•
•
•
•
Held up by electron degeneracy
About the size of the Earth R~5000km
Mass Typically 0.8M
Luminosity ~ .001 L
Thin layer of “normal” H
Degenerate Carbon
Some Famous White Dwarfs
• Sirius B
• 40 Eridani B
• Procyon B
All in binaries around nearby stars.
Establishes the WD is close and small.
Earth vs White Dwarf
Earth vs. Sun
Mass Radius Relation
1
R 3
M
As mass increases star gets smaller.
Like ball of foam.
WD Density
2 x1033
6


 1.5 x10 g / cc
8 3
4 3 4 x(7 x10 )
R
3
M
Water has a density of 1 g/cc
Lead 11 g/cc
Gold 19 g/cc
100,000 times density of gold!
NOT NORMAL MATTER!!
1 cubic centimeter masses one ton!
Surface Gravity
GM 7 x1011 x2 x1030
6
2
a 2 
 3x10 m / s
6 2
R
(7 x10 )
This is 300,000 gees
If you weigh 150lbs on Earth, you would weigh
45 million pounds on a White Dwarf!
What would happen to you and your spaceship?
Escape Velocity
2GM
2 x6.7 x1011 x2 x1030
13
6
Ve 


4
x
10

6
x
10
m/ s
6
R
7 x10
Speed of light is 3x108 m/s, so escape velocity is .02c.