Universe_CompositionFate_forclass1

Universe_CompositionFate_forclass1 - What is the Universe...

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What is the Universe made of? • Regular matter – Heavy elements 0.03% – Stars 0.5% – Free Hydrogen and Helium 4% • Neutrinos 0.3% • Dark Energy 70% • Dark Matter 25%
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Dark Matter Evidence • In 1930, Fritz Zwicky discovered that the galaxies in the Coma cluster were moving too fast to remain bound in the cluster according to the Virial Theorem KPNO image of the Coma cluster of galaxies - almost every object in this picture is a galaxy! Coma is 300 million light years away.
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Virial Theorem • Stable clusters of galaxies should obey this law: 2K = -U • where K= ! mv 2 is the Kinetic Energy • U = - ! GMm/r is the Potential Energy ( ! " 0.5) • Putting these together, we have M vir =v 2 r/ ! G. • Measure v and r and estimate the visible mass of the member galaxies (see previous lecture notes) • Compare the estimated mass to M virial • Zwicky found that the estimated mass was much smaller than M vir by about a factor of 50! • This implied the presence of dark matter.
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Dark Matter Evidence • Galaxy Rotation Curves Measure the velocity of stars and gas clouds from their Doppler shifts at various distances • Velocity curve flattens out! • Halo seems to cut off after r= 50 kpc NGC 3198 v 2 =GM/r where M is mass within a radius r Since v flattens out, M must increase with increasing r!
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Dark Matter Evidence • Hot gas in Galaxy Clusters • Measure the mass of light emitting matter in galaxies in the cluster (stars) • Measure mass of hot gas - it is 3-5 times greater than the mass in stars • Calculate the mass the cluster needs to hold in the hot gas - it is 5 - 10 times more than the mass of the gas plus the mass of the stars!
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Dark Matter Halo • The rotating disks of the spiral galaxies that we see are not stable • Dark matter halos provide enough gravitational force to hold the galaxies together • The halos also maintain the rapid velocities of the outermost stars in the galaxies
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Types of Dark Matter • Baryonic - ordinary matter: MACHOs, white, (faint) red or brown dwarfs, planets, black holes, neutron stars, gas, and dust • Non-baryonic - neutrinos, WIMPs or other supersymmetric particles and axions • Cold (CDM) - a form of non-baryonic dark matter
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This note was uploaded on 02/21/2011 for the course ASTR 2340 taught by Professor Rupalichandar during the Spring '10 term at Toledo.

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Universe_CompositionFate_forclass1 - What is the Universe...

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