MSU AST 207  Weighing the Universe with Supernovae (5 pages)
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Weighing the Universe with Supernovae
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Lecture Notes
 Pages:
 5
 School:
 Michigan State University
 Course:
 Ast 207  The Science of Astronomy
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Ast 207 F2009 Dec 09 Weighing the Universe with Supernovae 7 Dec Final exam Covers entire course with emphasis on 20th century cosmology Oct 28 to end of term Hwk 7 10 One 8 5 11 cheat sheet Mon 14th 3 00 5 00 1410 BPS large classroom next door Please fill out on line SOCT http rateyourclass msu edu Will close when grades are submitted Test answers are on angel Last class Review or SOAR Telescope Weighing the universe means to find mass density Why What is the universe made of Is there mass that we cannot see Distant supernovae Riess et al 2004 ApJ 607 665 How Mass in a large sphere surrounding us pulls on a galaxy on the surface Measure how much the galaxy slows Use supernovae to measure the time for the universe to expand What we will find Expansion of universe speeds up Dark energy is dominant Dark energy repulse whereas matter and radiation attract Ast 207 F2009 Cannon Ball Cannonball is shot out of cannon at speed v Kinetic energy is v2 v Gravity pulls on cannonball to slow the motion Potential energy is G M R Cannonball will escape if shot fast enough so that Define Density parameter KE PE PE KE 2 G M R v2 1 A cannonball is shot with 0 7 Will the cannonball escape Same question for 1 1 Do this on your own A B C D YY YN NY NN Ast 207 F2009 R M Ast 207 F2009 Dec 09 Universe Density Parameter Sphere expands and galaxy moves because universe expands Galaxy is moving at speed v Gravity pulls on galaxy to slow the motion v Kinetic energy is v2 R Potential energy is G M R Galaxy will escape if moving fast enough M KE PE Define Density parameter PE KE 2 G M R v2 Use Hubble s Law v HR PE KE 2 G M R3H2 Mass volume is mass density M volume 4 3 R3 PE KE 8 3 G H2 Does not depend on particular galaxy Ast 207 F2009 Does universe expand forever Density parameter PE KE 8 3 G H2 2 If the density parameter 0 7 will the universe expand forever Do this on your own A Y B N Ast 207 F2009 v R M Exam 3 Exam 3 35 30 9 25 10 3 4 20 1 2 15 1 4 10 5 20 Top 1 10 Top quartile Median Bottom
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