ASTR/PHYS 109 Dr. David Toback Lectures 20 & 21 1
Was due Today L21 Reading: (Unit 5) Pre-Lecture Reading Questions (PLRQ) All previous to Unit 4 revision: Let us know if you think you were misgraded Unit 4 Revision (if desired): Was due today before class. Unit 5: Was due before class End-of-Chapter Quizzes: Chapter 14 Parts A&B Papers: Papers 1 & 2 (Original): Let us know if you think you were misgraded Paper 1 and 2 Revisions: Working on these, but will be slow as we figure out how to integrate revised grades into Peerceptiv Paper 3: Back-Evaluations: Due tonight at 11:55PM 3
Unit 5: 1. Galaxies Today 2. Star Birth and Death Black Hole Formation 3. Properties of Black Holes 7
Galaxy Formation: Overview Big picture: What Galaxies look like How do galaxies form? When do galaxies form? 8
Where are we now in the history? Half a billion years after the bang 13
Visualize: As time progresses As the galaxy contracts, things can start moving very quickly 30
More time Passes Things start to flatten out Said differently, the flat part can continue, but the non-flat-part (the stuff going in other directions) gets bumped out of orbit 31
More time 32
Even more time 33
Even more time.. 34
Stable Galaxies The stuff in this stable state forms Stars: Call this a Galaxy Can give us disklike rotating galaxies Can also form other types like elliptical galaxies Galaxies often collide and get even more complicated 35
Fun video Move from the simple view of a galaxy forming to a more complete computer model from NASA How a disk galaxies gets created https://www.youtube.com/watch?&v=_ssc1gsqhds 36
Another fun video Andromeda tied to Simulation of a future collision the rocks between Andromeda and the Milky Way, where the two would create a combined galaxy http://people.physics.tamu.edu/toback/109/video/andromeda.avi 37
Move from what galaxies look like and how they form to WHEN galaxies form in the history of the Universe 38
When? Oldest observed galaxies appear about 500 million years after the bang Do we understand why this is? Use computer simulations to see when, after the Big Bang, galaxies form It turns out that if the Universe had exactly the same temperature everywhere it would take more than a hundred billion years to get even one galaxy What???? 39
Reason things might clump earlier? Clearly galaxies DID form before that, so SOMETHING must have caused them to start earlier Example of possible answer: If the temperature weren t perfectly uniform then we could get clumping earlier Go back to our trampoline analogy 40
Kids on a Trampoline The galaxies form shortly after we get that first big dent in space time If we start with all the kids equally spaced, then it will take longer to get that first collision If two of the kids happen to start slightly nearer each other, then those two are more likely to get a collision sooner and create the first dent sooner 41
Quantum Mechanics It turns out that when the Universe is really small, the effects of Quantum Mechanics can have a big effect on the smoothness of the Universe Can cause small variations in the temperature at different places in space Scientists gave this a cool name: Quantum fluctuations 42
So What? Different Temperature Variation in the amount of matter in different places A region with slightly more matter is more likely to be the place where matter clumps Thus, Quantum Fluctuations in the Early Universe could cause Galaxy formation to occur earlier in time 43
How would we look for this? How do we look at the temperature in the Universe? Study the Cosmic Background Radiation temperature distribution Any variations in different directions? 44
Look for Variation in the Cosmic Background Radiation Look at the full sky in a single map Temperature Map (i.e, different colors correspond to different temperatures) Stretch out a sphere onto a flat page Incredibly Uniform, but are there small variations? 45
Exactly the same everywhere? Subtract off the same amount everywhere What are we left with? The overall temperature is 2.728 degrees Kelvin The variation is very small T = 3.353 mk 46
Hotter and Colder? Colder here? Hotter here? T = 3.353 mk 47
What if we re moving? 48
Better Explanation Doppler effect of Moving away from this direction our speed relative to the rest frame of the photon background Earth is going around the sun at ~30 km/sec and the solar system is moving around the Milky Way at ~250 km/sec Moving toward this direction 49
The Cosmic Background Radiation Subtract off all the known effects and look for Variations Lots of small fluctuations (Spots) Everywhere Combining Quantum Mechanics and General Relativity predict where the galaxies form AND how long it takes 50
Lecture on Chapter 15 now complete 51
For Next Time L21 Reading: (Unit 5) Pre-Lecture Reading Questions (PLRQ) Unit 4 Revision (if desired) and Unit 5: Were due today before class, and will be graded soon End-of-Chapter Quizzes: Chapter 15 (if we finished Chapter 15, else just Chapter 14 Parts A&B) Papers: Paper 1 and 2 Regrades and Revisions: Working on these, but will be slow as we figure out how to integrate revised grades into Peerceptiv Paper 3: Back-Evaluations: Due tonight at 11:55PM General: Big Bang, Mis-graded Black on Big any Objects Assignment? and Black Let us Holes know 54
Full set of Readings So Far Required: BBBHNM: Chaps. 1-16 Recommended: TFTM: Chaps. 1-5 BHOT: Chaps. 1-7, 8 (68-85), 9 and 11 (117-122) SHU: Chaps. 1-3, 4(77-93), 5(95-114), 6, 7 (up-to-page 159) TOE: Chaps. 1-3 56