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 x1011 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 x1011 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.