1ASTR 1020: Stars & GalaxiesApril 25, 2008• Reading for next Wednesday: Chapter 13 – Extrasolar Planets.• MasteringAstronomy Homework on The Fate of the Universe is due April 30th.• Meet at Fiske Planetarium on Monday!• Final Exam: May 5, 4:30 – 7:00 pm; Chapters: 1.1-1.2, 4.1-4.4, 5, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23.Simulating the Big BangAstronomy In the NewsDeath Star Galaxy Black HoleNicholas BallasToday• Evidence for the Big Bang Theory• The results of InflationClicker Question: What is the earliest time in the Universe that we can directly observe?a) A few hundred million years after the Big Bangb) A few hundred thousand years after the Big Bangc) A few minutes after the Big BangClicker Question: What is the earliest time in the Universe that we can directly observe?a) A few hundred million years after the Big Bangb) A few hundred thousand years after the Big Bangc) A few minutes after the Big BangThis is the Cosmic Microwave Background.Era of Atoms and Galaxies(also called Epoch of Reionization)• About 1 billion years after Big Bang, first stars and galaxies start to form (z=10-20).• First stars in galaxies ionize gas surrounding the galaxies.2Did the Big Bang Really Happen?• How can we tell what happened so long ago?• 14 billion years ago• Mostly unobservable, not repeatable• Some of it at temperatures beyond our ability to even understand how physics works!Evidence for the Big Bang• 1) Expanding Universe• … run time backwards….2) The Cosmic Microwave Background (CMB)Observed all around usRemarkably uniform in all directions Æ something truly universalFits theory perfectly- the universe was once opaque and T~ 3000 K3) Helium is a minimum of 25%• Everywhere we look there is a minimumamount of helium Æ universal amountH Æ He at millions of degreesArgues whole universe was millions of degrees for a short timeClicker Question: If the current density of normal matter in the Universe were 10 times as great as it is now, we would expect to observea) More deuteriumb) Less deuteriumc) About the same amount of deuterium3Clicker Question: If the current density of normal matter in the Universe were 10 times as great as it is now, we would expect to observea) More deuteriumb) Less deuteriumc) About the same amount of deuteriumProtons & neutrons fuse to first produce deuterium and the deuterium fuse to produce helium. More baryons in early universe would have increased the rate of fusion and used up more deuterium so there would be less today.4) Ages of stars• Oldest stars ~ 13 billion years old• Consistent with models of expansion containing dark matter and dark energyInflation explains 3 hard-to-explain things• 1) Where do the little variations that grow to structure come from?• Quantum mechanics predicts tiny “quantum fluctuations” in the early universe• Too tiny in size to cause today’s structure• Inflation stretched them to the size needed to make the large structures (millions of light years across) that we see today• 2) Cosmic wallpaper and CMB on large scales are similar in all directionsOpposite sides of the universe- 28 billion light years apart, can’t yet have communicated what their temperatures, densities should be• These parts must have been in contact earlier, but then inflation pulled them apart4The Universe is Even Bigger than We Thought• Inflation predicts that the observable universe- 14 billion light years in radius- is only a very tiny fraction of the inflated universe3.) Universe is close to balancedMatter tends to curve space (Einstein’s general relativity)Universe with only 25% of the critical density will be curved outwards ÆDark energy tends to flatten it• Inflation my be responsible for stretching space, setting a balance between dark matter and dark energyA New Idea: Cosmological Branes• Extra dimensions folded into a membrane of spacetime.• Gravity “leaks through” added dimensions & is weakened.• Collision of “branes”triggers creation of new Universe (bubbles)?In inflation, our universe may be a minusculepart of one of many