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J B Lester

AST 201S - Stars and Galaxies University of Toronto Mississauga Chapter 17 Summary th Essential Cosmic Evolution, 5 Edition 1. Big Bang = start of the Universe from zero size • Mass and energy are related through E = mc 2 • Initial Universe was extremely hot • Expanding from this point the Universe cooled down 2. Some eras of the expanding Universe • Particle Era - 10−10s to 0.001 s after the Big Bang 12 – temperature greater than 10 K – energy becomes matter = protons, neutrons, electrons – antimatter should have been created, but we do not find it now – this charged gas (= plasma) is opaque to light • Fusion Era - 0.001 s to 5 minutes 12 9 – temperature drops from 10 K to 10 K – protons and neutrons fuse to create helium • Nuclei Era - 5 minutes to 380,000 years – too cool for fusion, but too hot for atoms • Era of Atoms 380,000 years to 1 billion year – protons and electron combine to form neutral atoms – Universe becomes transparent to light • Era of stars and galaxies - 1 billion+ years – gas had cooled enough for the first stars and galaxies to form 3. Tests of the hot Big Bank theory • Cosmic Microwave Background (CMB) – At 380,000 y, the Universe was a dense gas with a temperature of 3000 K emitting thermal radiation (Ch 5) – Radiation cannot escape from the Universe → must still be filling the Universe – The Universe has expanded for more than 13 billion years → thermal emission would be redshifted to a wavelength of ≈ 1 mm = microwaves (this was predicted in the 1940s) continued on page 2 AST201H5S – Chapter 17 Summary page 2 of 2 – CMB was discovered by accident in 1965 – CMB was confirmed by the COBE satellite in 1990 – CMB is being studied in detail by the WMAP satellite • Cosmic abundance of he
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