11ASTR 1020: Stars & GalaxiesApril 18, 2008• Reading: Chapter 23; section 23.1-23.2.• Extra credit: Fiske Planetarium shows every Thursday and SBO observing.2Astronomy In the NewsCorey Herrmann3Today• Chapter 22, Section 4: Dark Matter, Dark Energy, and the fate of the Universe • Preview of Chapter 23: The Creation of the Universe(the creation of all matter, light and energy)4Dark Matter and the Fate of the Universe• Expansion begins with the Big Bang• Several different models for Past and Future5 6What is the fate of the Universe?• Recollapse: crushing heat, destruction of all matter, ?rebirth?• Eternal expansion: cold, galaxies dimming– star formation slowing – everything winds up as a brown dwarf, black dwarf, neutron star or black hole27Some say the world will end in fireSome say with iceFrom what I’ve tasted of desireI hold with those who favor fireBut if I had to perish twiceI think I know enough of hateTo say that for destruction iceIs also greatAnd would suffice-- Robert Frost8Clicker Question: Which universe predicts the largest age for the universe today?a) Recollapsingb) Criticalc) Coasting(Ignore accelerating for now)9C) Coasting• Age of the universe is how far to the left the curves hit the horizontal axis (distance between galaxies =0)10Which is it?Is there enough dark matter to recollapse the universe?Baryonic matter: only a few percent of critical densityDark matter: only about 25% of what is neededUniverse is in between the “coasting” and “critical”modelsThe Universe will expand forever11Clicker Question: If there was really ZERO dark matter in the universe, which model would be the closest to reality?a) Coastingb) Criticalc) Recollapsing12• Baryonic matter is < 5 percentof the critical density.• Closest model would be the Coasting Model (no deceleration from gravity).313A New Twist for the 21stCentury• White dwarf supernovae: standard candles at z~1• Explosions bright enough to see very far away14Redshifts of the supernova plot their vertical position• Z=1 means about halfway down from the “NOW”level• expansion factor = 1+Z =215Their brightness plots their horizontal positionDimmer = more distant = longer ago• Supernovae are DIMMER than expected for a coasting universe•Universe is accelerating!16How 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!(Read “Einstein;s Biggest Blunder” p 679)17Accelerating model universe• Longest time since Big Bang (14 billion years)• Oldest stars are about 13 billion years old– other models fall short!• Universe will expand forever still……• Will there be more surprises to come????18• “Normal” Matter: ~ 4.4%– Normal Matter inside stars: ~ 0.6% – Normal Matter outside stars: ~ 3.8% • Dark Matter: ~ 25%• Dark Energy ~ 71%Summary: Contents of Universe419Chapter 23: In the VERY Beginning20Hot stuff!Everything in the Universe was hotter at earlier times, and then cooled as it expandedThe temperature at the earliest times was more than the energy we create in particle acceleratorsCosmology at the earliest times is explored via particle physics!21Matter and Energy•E=mc2• Matter and energy are the same, can transform from one to anotherMatter + antimatter
View Full Document
Unlocking...