Lecture21 - Signature Course UGS 303 (Fall 2009) The Dark...

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1 The History and Philosophy of Astronomy (Lecture 21: The Dark Side I: Dark Matter) Instructor: Volker Bromm The University of Texas at Austin Department of Astronomy Signature Course UGS 303 (Fall 2009) The Dark Side of the Universe • Big Q: What is the universe made of? • consensus view of early 21 st century (WMAP): - 4% normal matter (`baryons ʼ ) (stars, gas, people…) - 23% dark matter - 73% dark energy ``Deep into the darkness peering, long I stand there wondering, fearing. ʼʼ (E.A. Poe, The Raven ) • We don ʼ t know what > 90% of universe is made of !!! Fritz Zwicky: Astronomy ʼ s Mad Genius • Swiss national 1898 (Varna) – 1974 (Pasadena) • Professor at Caltech (1925+) • creative genius: - concept of supernova - neutron stars - dark matter (`missing mass ʼ ) • intense eccentricity (“spherical bastards”) 1933: Zwicky and the `Missing Mass ʼ • Coma cluster of galaxies - ~1,000 individual galaxies - 300 million lightyears away • Zwicky measures average (radial) velocities (from Doppler shift) - Result: ~1,000 km/sec • comparison with sum of visible (stellar) mass • BIG surprise: There must be 10 times more matter !
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2 1933: Zwicky and the `Missing Mass ʼ R V • measure: V and R • calculate required mass to hold cluster together: (Newton ʼ s constant) • Result for Coma: - need 10 times more mass than is visible! • For more than 30 years, no one else took this seriously! Vera Rubin: The Dark Side of Galaxies
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Lecture21 - Signature Course UGS 303 (Fall 2009) The Dark...

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