Big Bang, Black Holes, No Math

Transcription

1 ASTR/PHYS 109 Dr. David Toback Lectures 16 & 17 1

2 Was due Today L17 Reading: (BBBHNM Unit 2) Pre-Lecture Reading Questions: Let us know if you were misgraded on any submissions End-of-Chapter Quizzes: Chapter 7a and 7b Papers Paper 1: Text: Was due Wednesday Both Peerceptiv and TurnItIn on ecampus Reviews: Due Monday, Feb 26 th at 11:59PM Back-Evaluations: Due Wednesday, Feb 28 th at 11:59PM Paper 2: Will be assigned after we finish Chapter 8 Currently plan for text to be due Wednesday, March 7th 3

3 Heads Up: Paper 2 What is the evidence that Stars are made of Atoms? This will be the topic of Paper 2 In order to understand the evidence, we next talk about Atoms and how they work Will be assigned after we finish Chapter 8 4

4 So what? Why do we care about all the different kinds of atoms? What does this have to do with Stars and the Big Bang? The different mass and charge of each nucleus means that each atom has a different set of energy levels Each one has unique fingerprints! 19

5 Different energy levels for each different type of atom Fingerprinting the different atoms Hydrogen Helium Boron Can use light of different energies to identify atoms: Different Colors 20

6 Atomic Fingerprints Each atom produces a large number of different wavelengths with VERY SPECIFIC values Quantum Mechanics predicts ALL of them If you see all the ones you expect and none you don t, that gives you confidence 21

7 More on Fingerprinting Look at light from a light bulb with Hydrogen gas in the way Different lines will be absorbed by Helium Can now identify a mystery gas! 22

8 Overview of the story Big things are made from LOTS of small things Small things: The Fundamental Building Blocks of Nature What is the stuff in atoms ElectroMagnetism (electric charge) What holds electrons and protons together Quantum Mechanics Why atoms form the way they do Electron in orbits Atoms absorbing and emitting photons (light) Different TYPES of Atoms The Strong Force Keeping protons and neutrons together (atomic nuclei) Nuclear Physics and Chemistry Different atoms Different light Studying the Stars using their light Spectral lines of the atoms Atomic fingerprints The light we see from the stars Last Lecture This Lecture 23

9 Learning about Stars from their Light Can look at the light from the stars to learn about them Are they made of atoms? If so, what TYPE of atoms? How are stars formed? What makes them shine? 24

10 What is a Star? Our best understanding is that stars are giant balls of (mostly) hydrogen atoms The hydrogen interacts and produces the light we see Makes them shine What is the evidence for this? 25

11 Stars What would happen inside a giant ball of hydrogen? Atoms would fall to the center (due to gravity) and bash into each other What would that look like to us? Light from their interactions Next look at interactions 26

12 Hydrogen Interactions produce energy Proton Proton + Proton Deuterium + Anti-Electron + Neutrino Nuclear Reaction Anti- Electron Deuterium Proton Neutrino The Deuterium, neutrino and the Anti- Electron get energy in the reaction 27

13 More interactions More Energy Deuterium Proton + Deuterium Helium 3 + Photon Nuclear Reaction Photon Helium 3 Proton 28

14 Creating Stable Helium produces more Helium 3 Helium 3 + Helium 3 Helium Protons Nuclear Reaction Proton Helium 4 Helium 3 Proton 29

15 Stars Shining Nuclear interactions in the center of the star create lots of energy which is eventually emitted as light from the surface of the star Shines white (or yellow) 30

16 What else can we learn from the light? This light passes through other atoms of the star Light is absorbed by the outer atoms Spectral lines Tells us what the stars are made of 31

17 Looking at the Stars 32

18 Analyzing Absorption Spectra Each element produces a specific set of absorption (and emission) lines Using this information, we can study the composition of stars See only spectral lines for known atoms 33

19 Remarkable The Sun and stars are mostly made of Helium and Hydrogen Our Sun is made of the same stuff as all the other stars! The stuff out in the universe is made of the same stuff that is found here on Earth! 34

20 Even More Remarkable If all the stuff out there looks the same as the stuff here on Earth then: The particles out there (electrons, protons, photons etc.) are the same as they are here The laws of physics that govern putting together protons, nuclei and atoms are likely to be the same everywhere! Provides evidence that it s been this way for billions of years! 35

21 Now that we know what stars are made of and what they are SUPPOSED to look like, can we learn anything else? 36

22 What if the stars were MOVING? Can we tell? Yes! Doppler effect How? 37

23 Atoms with Different Speeds If an atom emits a photon it will correspond to an energy that reflects the change of two energy levels However if the atom is MOVING the light will be shifted to a different color 38

24 Observing an Atom Atom Emitting Light Not Moving to the right Can use this to study the motions of the stars 39

25 Looking at the Stars Provides additional evidence stars are made of atoms 40

26 Lecture on Chapter 8 now complete 41

27 Paper 2 Abbreviated description: What is the evidence that Stars are made of Atoms? More detail on Peerceptiv, you REALLY need to read ALL the instructions Explain it to someone who isn t taking the class (no jargon) Format: Introduction paragraph Lawyers opening arguments at a Trial ~1 paragraph per piece of evidence/talking point The case at a Trial Conclusion paragraph that ties it together Lawyers closing arguments at a Trial 42

28 Outline for Unit 2: 1. Light and Doppler Shifts Done 2. Gravity, General Relativity and Dark Matter Done 3. Atomic Physics and Quantum Mechanics Done 4. Nuclear Physics and Chemistry Done 5. Temperature and Thermal Equilibrium Next time 43

29 Prep For Next Time L17 Reading: (BBBHNM Unit 2) Pre-Lecture Reading Questions: Let us know if you were misgraded on any submissions End-of-Chapter Quizzes: If we finished Chapter 8 then End-of-Chapter Quiz parts 8a and 8b (else, just 7a and 7b) Papers Paper 1: Text: Was due Wednesday Both Peerceptiv and TurnItIn on ecampus Reviews: Due Monday, Feb 26 th at 11:59PM Back-Evaluations: Due Wednesday, Feb 28 th at 11:59PM Paper 2: Will be assigned after we finish Chapter 8 Currently plan for text to be due Wednesday, March 7th 46

30 Full set of Readings So Far Required: BBBHNM: Chap 1-9 Recommended: BHOT: Chap. 1-6, 9 and 11 ( ) SHU: Chap. 1-3, 6 and 7 (upto page 153) TOE: Chap. 1 47