Exams will be returned on Thursday 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->He Temperature and Density Rise in Center Star gets more luminous He

Electron Degeneracy 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 Helium Burns in the Center Starts to Development Dead C Core

Red Giants

Nucleus Earth Orbit

Red Supergiant Meanwhile, down in the core, the C is becoming degenerate. Luminosity is becoming so great it blows the H envelope into space. H H->He He->C C

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 As mass increases star gets smaller. Like ball of foam.

WD Density 1 cubic centimeter masses one ton! 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 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 Speed of light is 3x108 m/s, so escape velocity is .02c.