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Transcript
ASTR 101 General Astronomy: Stars & Galaxies Three models for fate of universe in a matter-dominated Universe REVIEW ANNOUNCEMENTS MIDTERM III: Monday, May 4th Midterm make-up: Tue, May 5th, 11am Last Astronomy public talk, May 8th (up to 3% Extra class credit – (see Blackboard announcement for details) CLOSED Friday class: REVIEW for Midterm III (led by TA Melissa Hoffmann) Very important diagram measure of “expansion factor of Universe” OPEN REVIEW A. Recollapsing (closed) REVIEW B. Critical (flat) NOW Hubble constant NOW sets how fast universe is expanding NOW Clicker Question Which model predicts the youngest age for the universe today? SIZE “Average distance between galaxies” FLAT TIME C. Coasting (open) Big Bang = when distance zero Clicker Question • A. Recollapsing • Age of universe is how far to left curves hit horizontal axis (distance between galaxies = 0) What determines the future average distance between galaxies? A. The rate of expansion, with a slower expansion rate meaning a greater average distance B. The rate of expansion, with a faster expansion rate meaning a greater average distance C. Only on the density of matter in the universe. Clicker Question What determines the future average distance between galaxies? A. The rate of expansion, with a slower expansion rate meaning a greater average distance B. The rate of expansion, with a faster expansion rate meaning a greater average distance C. Only on the density of matter in the universe. Clicker Question Which model has the slowest future rate of expansion? A. Recollapsing B. Critical C. Coasting Clicker Question Which solution is realized? Which model has the slowest future rate of expansion? Is there enough dark matter to recollapse the universe? A. Recollapsing Baryonic matter: only a few % of critical density B. Critical Dark matter: only about 25% of what is needed C. Coasting The Universe will expand forever … and with an unexpected twist… A New Twist for the Century • Scientists using white dwarf supernovae to measure distances discovered something quite strange 21st Using supernovae to determine the fate of the Universe • Redshifts of the supernovae gives their vertical position – Space has stretched since they gave off their light • Apparent brightness gives their horizontal position – Dimmer=more distant = high lookback Supernovae are not consistent even with the expectations of a coasting universe!!! How can the universe be accelerating??? A force that counteracts gravity? “Dark energy”– outweighs every other form of mass/energy! Truly an unknown force in all of physics The Cosmological Constant actually exists! Universe is accelerating?!?! Four models for fates of universe ( Einstein s Greatest Blunder ) The Fate of the Universe Eternal expansion: CLOSED – Cold, galaxies dimming – Star formation slowing – Everything winds up as a brown dwarf, black dwarf, neutron star or black hole FLAT OPEN ACCELERATING Clicker Question Clicker Question What is meant by “dark energy”? What is meant by “dark energy”? A. The energy associated with dark matter through E=mc2 B. An unknown form of energy that counteracts gravity and causes the expansion of the universe to accelerate. C. Any unknown force that acts like gravity D. Highly energetic particles that are believed to constitute dark matter E. The total energy in the universe after the Big Bang but before the first stars A. The energy associated with dark matter through E=mc2 B. An unknown form of energy that counteracts gravity and causes the expansion of the universe to accelerate. C. Any unknown force that acts like gravity D. Highly energetic particles that are believed to constitute dark matter E. The total energy in the universe after the Big Bang but before the first stars At LAST: In the very Beginning…