Transcript Slide 1
Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr. David Toback Lecture 22 & 23 Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 1 Holes, No Math Topic 2: Stars Was due Today – L23 • Reading: – (Unit 5) • Pre-Lecture Reading Questions: – Unit 5 Revision (if desired): Stage 1 • End-of-Chapter Quizzes: – Chapter 15 • Papers: – Paper 3 Revision (if desired): Stage 1 due Wednesday • Honors Papers: – (Stage 2) – Final paper due on the last day of class Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 2 Holes, No Math Topic 2: Stars Unit 5: Big Objects 1. Galaxies 2. Star Birth and Death 3. More on Black Holes It turns out that the way Galaxies and Stars form is very similar… start there The way stars “die” depends on the star itself… sometimes they die to form a Black Hole Today Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 3 Holes, No Math Topic 2: Stars Important Buzz Words Wanted to make sure we explained some of the important buzz words in astronomy: – Red Giant – Supernova – White Dwarf – Neutron Star – Black Hole Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 4 Holes, No Math Topic 2: Stars Today’s Lecture • A star is born • Nuclear reactions and gravity keep stars alive and make them shine • The life of stars: shining and converting hydrogen into heavier elements • Life and death of stars like our Sun • Life and death of massive stars Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 5 Holes, No Math Topic 2: Stars Where are we now in the history? A few hundred million years after the bang, stars start forming Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 6 Holes, No Math Topic 2: Stars Quick Summary of Galaxy Formation • Half a million years after the Big Bang we have lots of neutral stuff floating around in space • Half a billion years after the bang the stuff has clumped into galaxies Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 7 Holes, No Math Topic 2: Stars Stellar Clumps • The galaxies start as giant spinning areas of neutral, massive stuff kept together by gravity • Eventually, local areas that orbit around the center of the galaxy are close enough to each other that they also start clumping due to gravity • Eventually, the hydrogen and helium atoms can start to interact with each other Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 8 Holes, No Math Topic 2: Stars Star Formation • This is some text.. Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 9 Holes, No Math Topic 2: Stars Step 2 • More… Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 10 Holes, No Math Topic 2: Stars Step 3 • This is some text… Beginnings of planets! Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 11 Holes, No Math Topic 2: Stars Stars have some things in common with Spiral Galaxies Will be the planets Will be the star Gee… kinda looks like Saturn also… Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 12 Holes, No Math Topic 2: Stars Describing Stars We tend to use metaphors to describe Stars 1. Can think of them like people: They have a birth, a life and a death 2. Can think of them like a car: They run on “fuel,” and “die” when they run out of fuel 3. Can think of them like a balloon: A giant collection of atoms that are “forced” to stay inside the balloon walls Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 13 Holes, No Math Topic 2: Stars Proto-stars •Gravity brings together the stuff in a galaxy that has mass •When the atoms (mostly hydrogen and a little helium) get close enough they start moving quickly into the center •However, need to get really close before they will interact Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 14 Holes, No Math Topic 2: Stars Low energy (temperature) hydrogen reactions Proton Electro-magnitism Reaction Same charges repel Proton=Hydrogen Proton Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 15 Holes, No Math Topic 2: Stars A Star is Born • When there are enough atoms, the large amount of mass makes the pull to the center so strong that the hydrogen starts moving quickly into the center become higher temperature • When atoms reach a high enough temperature (10 Million Kelvin) they start to have nuclear interactions Creates the light we see (makes stars shine) Atoms inside the Sun don’t move in the same way the Earth orbits outside it Call this a star Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 16 Holes, No Math Topic 2: Stars Hydrogen Reactions at high Temperatures Proton Proton + Proton Deuterium + Electron + Neutrino Anti-Electron Nuclear Reaction Deuterium Proton=Hydrogen Neutrino This is what we call Fusion Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 17 get LOTS of energy Holes, No MathOut-going particles Topic 2: Stars Proton The Life and Death of Stars A star’s life is effectively a battle between: 1.Gravity trying to crush everything into a tiny point 2.The nuclear interactions “opposing” the gravity Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 18 Holes, No Math Topic 2: Stars Only in the center of Stars • The center of a star is called the core • This is where the particles have the highest energy and density This is where all the fusion occurs Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 19 Holes, No Math Topic 2: Stars Where does the energy come from? • Mass of Deuterium is smaller than the mass of two protons • So what? E=mc2, so the “mass energy” gets converted into kinetic energy in the collision Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 20 Holes, No Math Topic 2: Stars Hydrogen Reactions Proton Proton + Proton Deuterium + Electron + Neutrino Anti-Electron Nuclear Reaction Deuterium Proton=Hydrogen Neutrino Fusion produces particles with LOTS of Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 21 Holes, No Mathenergy Topic 2: Stars Proton Hydrogen and Deuterium Deuterium Proton + Deuterium 3He + Photon Again, lots of energy to the particles Nuclear Reaction Photon 3He Proton Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 22 Holes, No Math Topic 2: Stars Creating Stable Helium 3He 3He + 3He 4He + 2 Hydrogens More energy is released Nuclear Reaction Hydrogen 4He 3He Hydrogen Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 23 Holes, No Math Topic 2: Stars Nuclear “Burning” • In each nuclear reaction additional energy is released Some of the energy “turns into” photons (and neutrinos) – This is what makes stars shine Some energy goes into the increased speed of the atoms – This is what keeps the star from crushing itself How? Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 24 Holes, No Math Topic 2: Stars Thinking of a Star as a Balloon • The hydrogen and helium are the gas inside the balloon, the fusion speeds them up so they “try” to leave • The gravity is what keeps it all together, like the walls of the balloon Gravity holds it together Hydrogen and Helium gas Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 25 Holes, No Math Topic 2: Stars Small speed objects can’t leave the Earth Look at the different things that can happen at various speeds on various size “heavenly bodies” Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 26 Holes, No Math Topic 2: Stars Another example with the same speed bullet but on the Moon Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 27 Holes, No Math Topic 2: Stars If we move to an asteroid, then it CAN leave Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 28 Holes, No Math Topic 2: Stars Can build things that shoot fast enough to leave the Moon Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 29 Holes, No Math Topic 2: Stars Why doesn’t the Balloon deflate or pop? If an atom has a high speed or there is only small gravity (star is small mass) then the atom will leave the star Small Gravity Hydrogen and Helium Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 30 Holes, No Math Topic 2: Stars Why doesn’t the Balloon deflate or pop? • If gravity is strong (large mass star), or the speed is small then gravity drags the atoms back to the center – Acts “like” the walls of a balloon – The more massive the star the stronger the walls – Atoms don’t leave Large Gravity Hydrogen And Helium Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 31 Holes, No Math Topic 2: Stars A Stable Star • The nuclear reactions speed up the atoms – “Try to make the balloon pop” – Create light • Gravity pulls it back together • The size of the balloon depends on this balance Gravity Nuclear Reactions – Can stay stable for billions of years Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 32 Holes, No Math Topic 2: Stars The Fuel of a Star The Hydrogen and Helium provide the “fuel” that both: 1. Creates the light we see 2. Keeps the star stable Converts light atoms into heavy atoms Big Bang, Black Massive Things: Galaxies, Stars and Black Holes Holes, No Math Topic 2: Stars 33 The Life of a Star The star starts as a “ball” of mostly hydrogen, with the fusion in the core What happens when it runs out of Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 34 fuel? Holes, No Math Topic 2: Stars What happens when the Hydrogen Runs out? • Without hydrogen fuel to make things “expand,” gravity crushes atoms closer and closer together – It takes a temperature of 100 million Kelvin to fuse Helium, this may not happen for many stars • From there what happens next depends on the “mass” of the star Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 35 Holes, No Math Topic 2: Stars Start with Stars like our Sun • Mid-sized stars (between 8% and 8 times the mass of our Sun) all typically have a similar life • Smaller than 8% of the Sun won’t get hot enough to fuse hydrogen – Isn’t really a star at all – Call this a brown dwarf • More than 8 times the mass of our Sun complicated things can happen Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 36 Holes, No Math Topic 2: Stars The Life and Death of our Sun • Sun is using its hydrogen to create light • Helium produced falls to the center (the core) • Today: Core only about 15 million Kelvin not hot enough to convert Big Bang,helium Black Massive Things: Galaxies, Stars and Black Holes 37 into Carbon Holes, No Math Topic 2: Stars Future: White Dwarf When most of the hydrogen is used up, the core gets crushed Eventually the atoms get REALLY close to each other and the strength of the repulsion between the electrons from quantum mechanics is so big that it balances out the gravity Outer part becomes a Red Giant and then diffuses into space – Inner part stabilizes • Call this a “White Dwarf” Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 38 Holes, No Math Topic 2: Stars Lots of White Dwarfs in the Universe • Hot core creates heavy elements • Can shine for quite awhile – This is why we call it “white” • Really dense: An object with the mass of the Sun shrunk to about the size of the Earth – This is why we call it a “dwarf” • How dense? A pair of standard dice would weigh about 5 tons Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 39 Holes, No Math Topic 2: Stars White Dwarf Black Dwarf • Eventually a white dwarf star runs out of the rest of its fuel (nothing left but iron) and it stops emitting light • Call this a “Black Dwarf” • However, predictions are that it takes so long for this to happen that none should exist… none observed Big Bang, Black Massive Things: Galaxies, Stars and Black Holes Holes, No Math Topic 2: Stars 40 Next move to heavier stars… Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 41 Holes, No Math Topic 2: Stars The Life of a Heavy Star • For heavy stars the first part of their life is the same as for lighter stars: after the hydrogen runs out, gravity crushes the core • What is different is that for heavy stars there is so much mass that gravity can continue to crush the core, and the temperature can rise significantly • For stars with more than 8 times the mass of the Sun, the core can reach a temperature of 100 million Kelvin, and helium fusion can start • Helium can fuse to make heavier elements Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 42 Holes, No Math Topic 2: Stars Stages in a Massive Star’s Life Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 43 Holes, No Math Topic 2: Stars Converting Helium to Beryllium 4He 4He 4 + 4He4 8Beryllium Nuclear Reaction 8Beryllium 4He Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 44 Holes, No Math Topic 2: Stars Converting Beryllium to Carbon 8Beryllium 8Beryllium + 4He Nuclear Reaction 4He 12Carbon + Photon 12Carbon Photon Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 45 Holes, No Math Topic 2: Stars The Most Massive Stars •For the heaviest stars, after the helium is used up can start fusing Carbon •Then Neon •Keep going…Get “shells” of the various types of atoms •This is where the atoms WE/Earth get Bigcreated Bang, Black Massive Things: Holes, No Math Galaxies, Stars and Black Holes 46 Topic 2: Stars How Long do Stars Live? Weird: stars with huge mass die faster than lighter stars. Why? • The more massive the star, the more it crushes atoms in the center and raises their temperature • The hotter/denser the star, the faster the nuclear reactions occur The sooner it burns out – Some stars can last as little as a hundred million years Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 47 Holes, No Math Topic 2: Stars Death of Very Massive Stars • If the star is much more massive than our Sun it runs out of fuel quickly – 1x Sun ~10 billion years – 10x Sun ~30 million years – 100x Sun ~100,000 years • Different things happen as it runs out of fuel gravity is so strong it Big Bang, Massive Things: Galaxies, and Black Holes 48 can Black REALLY crush theStars star Holes, No Math Topic 2: Stars More Crushing Neutron Star • After the fuel runs out, if the mass of the star is large enough, gravity crushes the atoms into each other • The electrons are pushed so close to the protons that they start to interact – Turn into Neutrons (more on the physics of this interaction in Chapter 19) • The star turns into a giant ball of neutrons about the size of Manhattan Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 49 Holes, No Math Topic 2: Stars Creating Neutron Stars Proton + Electron Neutron + Neutrino Neutrino (leaves the star) Electron Up Quark Down Quark Down Quark Up Quark Proton Neutron Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 50 Holes, No Math Topic 2: Stars Neutron Stars • Neutrons don’t like to be “too close” to each other because of Quantum Mechanics star can stabilize • In this process the star has collapsed from the size of the Earth into a ball of neutrons just a few kilometers across • Incredibly dense! – Billions of tons per cubic inch – A marble made from neutron star material would weigh the same as the Earth Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 51 Holes, No Math Topic 2: Stars The crushing… • The inner part of the star is quickly crushed into a neutron star • What happens to the outer part? Falls towards the center! • Hits the dense neutron core and bounces back into space as a giant explosion Big Bang, Black Massive Things: Galaxies, Stars and Black Holes Holes, No Math Topic 2: Stars 52 Huge Explosion = Supernova • The explosion can be so big that it can shine as bright as 10 billion suns for a couple of weeks • The temperatures in the explosion are so high and the atoms are so densely packed that really heavy atoms can be created and then blown into space – This is how we get stuff like uranium on the Earth • We call the “remnants” of supernovas “nebulae” Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 53 Holes, No Math Topic 2: Stars Moving Towards Black Holes • If the remaining neutron star has a “critical mass” (about 3MSun) it can continue to collapse • Nothing left to oppose the crush of gravity! Continues to collapse until it becomes a Black Hole Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 54 Holes, No Math Topic 2: Stars For Next Time – L22 • Reading: – (Unit 5) • Pre-Lecture Reading Questions: – Unit 5 Revision (if desired): Stage 1 • End-of-Chapter Quizzes: – Chapter 16 if we finished Chapter 16 (else just Chapter 15) • Papers: – Paper 3 Revision (if desired): Stage 1 due Wednesday • Honors Papers: – (Stage 2) – Final paper due on the last day of class Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 55 Holes, No Math Topic 2: Stars For Next Time – L23 • Reading: – (Unit 5) • Pre-Lecture Reading Questions: – Unit 5 Revision (if desired): Stage 2 • End-of-Chapter Quizzes: – Chapter 16 if we finished Chapter 16 (else just Chapter 15) • Papers: – Paper 3 Revision (if desired): Stage 1 due Wednesday • Honors Papers: – (Stage 2) – Final paper due on the last day of class Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 56 Holes, No Math Topic 2: Stars Full set of Readings So Far •Required: –BBBHNM: Chaps. 1-17 •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 Big Bang, Black 57 Massive Things: Galaxies, Stars and Black Holes Holes, No Math Topic 2: Stars Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 58 Holes, No Math Topic 2: Stars Clicker Question Why do stars shine? a) When atoms fall back to their lowest energy level, they give off light b) Gravity is pushing atoms to fuse c) Nuclear reactions d) Heavy nuclei Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 59 Holes, No Math Topic 2: Stars Clicker Question What is the main reason the atoms in a star don't just all fall to the center of the star? a) Because of the surface of the star keeps them from falling to the center the same way the surface of the Earth keeps things from falling to the center b) Because all the other atoms are in the way c) Because of the pull of gravity d) None of the above Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 60 Holes, No Math Topic 2: Stars Clicker Question What are the two main interactions in stars and how do they relate to each other? 1. Gravity and nuclear fusion 2. Gravity and degeneracy pressure 3. Nuclear fusion and degeneracy pressure Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 61 Holes, No Math Topic 2: Stars The Life of a Star Continued… As the hydrogen gets used up the core “ball” becomes a smaller ball of mostly helium Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 62 Holes, No Math Topic 2: Stars The “Burning” Process • At the beginning of a stars life, most of the atoms are hydrogen they get converted to helium first • Then the helium starts getting converted into heavier elements like carbon, oxygen and iron Produces many of the heavy elements that will go into the universe after it dies Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 63 Holes, No Math Topic 2: Stars Death of Stars When the hydrogen “fuel” runs out different things happen for very massive stars and small mass stars separately Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 64 Holes, No Math Topic 2: Stars Next look at the nuclear reactions that keep the star from getting “crushed” by gravity Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 65 Holes, No Math Topic 2: Stars Prep for Next time – L23 • Reading: – Chapter 18 • Pre-Lecture Reading Questions: – Chapter 18 • End-of-Chapter Quizzes: – If we finished Chapter 16 then end-ofchapter quiz 16 (else just through Chapter 15) • Papers: – Paper 2 Revision: Was due before class today. Let us know if you were mis-graded – Paper 3: Calibrations, reviews and SelfBig Bang, Black Massivedue Things: Galaxies, Stars and Black Holes 66 assessment Wednesday before class Holes, No Math Topic 2: Stars Was due Today – L24 • Reading: – Chapter 18 • Pre-Lecture Reading Questions: – Chapter 18 • End-of-Chapter Quizzes: – Chapter 15 was due, but I’ll give extensions since Chapter 14 was busted. – You need to go back and check Chapter 14. Many of you need to go back and fix the wrong answers you were accidentally getting credit for • Papers: – Paper 3: Was due today. One of the calibrations was busted. I’ll fix that soon. After I do that, I’ll open up a chance for Revisions Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 67 Holes, No Math Topic 2: Stars Prep for Next time – L24 • Reading: – Chapter 18 • Pre-Lecture Reading Questions: – Chapter 18 • End-of-Chapter Quizzes: – If we finished Chapter 16 then end-of-chapter quiz 16 (else just through Chapter 15) – You need to go back and check Chapter 14. Many of you need to go back and fix the wrong answers you were accidentally getting credit for • Papers: – Paper 3: Was due today. One of the calibrations was busted. I’ll fix that soon. After I do that, I’ll open up a chance for Revisions Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 68 Holes, No Math Topic 2: Stars Prep For Next Time – L10 • Note: May change depending on how far we get in lecture • Reading: –BBBHNM: All reading through Chapter 18 • Reading Questions: – All reading questions through 18 • eLearning Quizzes: – If we finished Chapter 16 then end-of-chapter quiz 16 (else just through Chapter 15) • Papers: – Paper 3 revisions text (if desired) due before class on Monday – Paper 2 revisions (if any) calibration, reviews and self-assessment due before class on Monday Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 69 Holes, No Math Topic 2: Stars Was due today– L11 • Reading: –BBBHNM: All reading through Chapter 18 •Reading Questions: – All reading questions through 18 • eLearning Quizzes: – Through Chapter 16 • Papers: – Text of Paper 3 revisions (if desired) were due before class – Paper 2 revisions (if any): calibration, reviews and self-assessment due before class Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 70 Holes, No Math Topic 2: Stars Prep for Today (Is now due) – L22 • Reading: – BBBHNM 17 • Reading questions: – Chapter 17 • End-of-Chapter Quizzes: – Chapter 15 • Paper Stuff – Paper 2 Revision: Calibrations and Review were due before class – Paper 3: Calibrations and Review were due before class Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 71 Holes, No Math Topic 2: Stars Prep For Next Time – L11 • Note: May change depending on how far we get in lecture • Reading: –BBBHNM: All reading through Chapter 19 • Reading Questions: – All reading questions through 19 • eLearning Quizzes: – If we finished Chapter 16 then end-of-chapter quiz 16 (else just through Chapter 15) • Papers: – Rest of Paper 3 assignment (if you resubmitted) due before class on Tuesday Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 72 Holes, No Math Topic 2: Stars Prep for Next Time – P21 • Reading – BBBHNM 17 • Reading questions – Chapter 17 • End-of-Chapter Quizzes – If we finished Chapter 16 then end-of-chapter quiz 16 (else just 15) • Papers – Paper 2 Revision: Calibrations and Review were due before class – Paper 3: Calibrations and Review were due before class – Paper 4: Will assign paper 4 next time Big Bang, Black Massive Things: Galaxies, Stars and Black Holes Holes, No Math Topic 2: Stars 73 Prep for Next Time – P22 • Reading – BBBHNM 17 • Reading questions – Chapter 17 • End-of-Chapter Quizzes – If we finished Chapter 16 then end-of-chapter quiz 16 (else just 15) • Papers – Paper 2 Revision: Calibrations and Review were due before class – Paper 3: Calibrations and Review were due before class – Paper 4: Will assign paper 4 next time Big Bang, Black Massive Things: Galaxies, Stars and Black Holes Holes, No Math Topic 2: Stars 74 Full set of Readings So Far •Required: –BBBHNM: Chaps. 1-17 •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 Big Bang, Black 75 Massive Things: Galaxies, Stars and Black Holes Holes, No Math Topic 2: Stars Future: The Red Giant Phase When most of the hydrogen is used up, the core gets crushed Helium falling towards the center speeds up and interacts Heats up the hydrogen in the outer shell Inflates to giant red shell that emits red light Big Bang, Black Massive Things: Galaxies, Black Earth Holes 76 Bigger than the sizeStars ofandthe Holes, No Math Topic 2: Stars White Dwarf Eventually the atoms get REALLY close to each other and the strength of the repulsion between the electrons from quantum mechanics is so big that it balances out the gravity – Outer part is blown away • Planetary Nebula – Inner part stabilizes • Call this a “White Dwarf” Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 77 Holes, No Math Topic 2: Stars Shouldn’t a Star just Collapse? • Why don’t the atoms just fall to the center of the star? • Do they orbit? • If the star is giving off light aren’t the atoms losing energy, so they should fall in Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 78 Holes, No Math Topic 2: Stars Today’s Lecture •Galaxies Form •Stars Form… •Stars Die… and die in different ways Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 79 Holes, No Math Topic 2: Stars The life and death of our Sun Our Sun will go through a Red Giant phase in about 5 billion years Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 80 Holes, No Math Topic 2: Stars Our Sun Today •Sun is using its hydrogen to create light •Helium produced falls to the center (the core) – Core is not hot enough to convert helium into Carbon Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 81 Holes, No Math Topic 2: Stars For Next Time Topics • Galaxy Formation Done • Stars Done • Black Holes Next Reading for Next time: BBBHNM: Chap 17 Full reading for Unit 5: • BBBHNM: Chaps. 1-17 • 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 (upto-page 159) • TOE: Chaps. 1-3 Lecture prep: Turn in on eLearning Two questions fromGalaxies, ChapterStars 17 you to 82 Big Bang, Black Massive Things: and want Black Holes Holes, No know Math the answer to Topic 2: Stars Shouldn’t a Star just Collapse? • Atoms in stars give off lots of light as energy • If the atoms are losing energy, why don’t they just slow down and have everything fall to the center of the star? Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 83 Holes, No Math Topic 2: Stars A giant lump of atoms? • Why doesn’t everything just fall to the center of the Earth? • The Earth is solid, but stars aren’t –Earth is made of iron and heavy atoms Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 84 Holes, No Math Topic 2: Stars The Reading So Far and For Unit 5 Reading for Unit 5: • BBBHNM: Chaps. 15-17 • SHU: 4(87-93) • TOE: 3 • BHOT: 8(76-85) Full reading through Unit 5: • BBBHNM: Chaps. 1-17 • 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) • Bang, TOE:Black Chaps. 1-3 Big Massive Things: Galaxies, Stars and Black Holes 85 Holes, No Math Topic 2: Stars Other Stuff • Q-Drop date is tomorrow – No final – Only papers 1-5 (due last day of class) • Elearning: – Unit 5 in progress • Make sure you pick up the latest version of the online textbook!!! Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 86 – Been updating it all semester Holes, No Math Topic 2: Stars Papers 1 and 2 • Paper 1 is done • Paper 2 grades are on eLearning – Working on getting the revised grades fixed – Paper 2 Revision is done Big 87 Bang, Black Massive Things: Galaxies, Stars and Black Holes Holes, No Math Topic 2: Stars Papers 3,4 and 5 • Paper 3: – Let us know if you think you have been mis-graded – Revisions now open • Paper 4: – Assigned after we start Chap 17 – Probably today – Due 1 week after we finish Chap 17 • Paper 5 (last paper, no final) – Assigned after we start Chap 20 Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 88 Holes, No Math Topic 2: Stars Other Stuff • Elearning: –Unit 5 in progress • Make sure you pick up the latest version of the online textbook!!! –Been updating it all semester Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 89 Holes, No Math Topic 2: Stars Examples • Our sun: Has another ~5 billion years before it goes through a Red Giant Phase • Others can last as little as a hundred million years Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 90 Holes, No Math Topic 2: Stars The Life and Death of Stars Small Star (Red Giant) White Dwarf Brown Dwarf Big Star (Supergiant) Explodes (Supernova) Neutron Star Black Hole Slightly more complicated than this… Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 91 Holes, No Math Topic 2: Stars Writing Assignments Short Assignments 1 & 2 Re-do’s are still possible. Want to revise again? Talk to me eLearning: Unit 4 now due Need to be working on Unit 5 Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 92 Holes, No Math Topic 2: Stars Papers AFTER Paper 2 Two options 1.Two short papers like the first one • One on Black Holes (due one week after we finish Black Holes) • One on Dark Matter (due last day of class) 2.Research Paper If you want this option Stage 1 must be approved ASAP • Was due last week • Final paper due the last day of th Big Bang, class, Black Massive Things: Galaxies, Stars and Black Holes 93 Tuesday Dec 8 Holes, No Math Topic 2: Stars For Next Time • More on the properties of Black Holes… Full reading for Unit 5: • BBBHNM: Chaps. 1-17 • TFTM: Chaps. 1-5 • BHOT: Chaps. 1-7, 8 (68-85), 9 and 11 (117-122) • SHU: Chaps. 1-3, 4(77-93), 5(95114), 6, 7 (up-to-page 159) • TOE: Chaps. 1-3 Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 94 Holes, No Math Topic 2: Stars Why do we call it a black hole? Look at objects this big Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 95 Holes, No Math Topic 2: Stars Escape Velocity • The escape velocity for the Earth is about 11.2 km/sec • The escape velocity for the sun is about 620 km/sec • The escape velocity of a neutron star is about half the speed of light! Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 96 Holes, No Math Topic 2: Stars Why do we call it a Black Hole? A Black Hole is so dense that it’s escape velocity is GREATER than the speed of light light can no longer escape! More on this soon… Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 97 Holes, No Math Topic 2: Stars Wait a Billion Years After less than ~1 billion years, galaxies and the first stars start to form Formation of the first stars Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 98 Holes, No Math Topic 2: Stars Remaining Lectures • Two lectures left: Today and Thursday – Stars and Black Holes – Won’t get back to Inflation and Dark Energy (Lectures posted) • Recitation tomorrow as usual • Extra recitation at the Dixie Chicken at 2:00 PM tomorrow (Wednesday) Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 99 Holes, No Math Topic 2: Stars Remaining Assignments • Writing Assignments Due Thursday – However, you may turn it in, via email, on Monday – If you want to revise your paper you’ll need to pick it up from me directly • Don’t forget to finish your WebCT stuff Big Bang, Black Massive Things: Galaxies, Stars and Black Holes100 Holes, No Math Topic 2: Stars • Textbook? • BHOT 8 starting on page 76. • SHU 4, 5 • SHU 8 for MACHOs (need this?), 9 Dark Matter (Cold or hot?) • SHU 10 is Quasars… • SHU 11: In search of black holes • TOE 3, 4 • TCP 17 Reading: – TOE: 3 – BHOT: 8 – SHU: 4, 7 – TCP 16 and 17 – Others??? Big Bang, Black Massive Things: Galaxies, Stars and Black Holes101 Holes, No Math Topic 2: Stars Summary of the Buzz Words in the Newspapers • White Dwarf • Brown Dwarf • Neutron star • Supernova • Black Hole Big Bang, Black Massive Things: Galaxies, Stars and Black Holes102 Holes, No Math Topic 2: Stars TCP 17 cont… • Once the critical mass is reached nothing can hold back gravity and it collapses on itself and becomes a black hole. • This stretches space time • Cool pictures on page 529 Big Bang, Black Massive Things: Galaxies, Stars and Black Holes103 Holes, No Math Topic 2: Stars TCP 17 cont… • How black holes are formed • A black hole originates in the collapse of the iron core that forms just prior to the supernova of a very high mass star • Any star born with more than about 8MSun dies in a supernova (previous lecture), but most of the star’s mass is blown into space by the explosion. • As a result most of the collapsed cores left behind by most supernovae become neutron stars • However, if the supernovae doesn’t blow away too much of the mass the remaining neutron star can have enough mass so that the neutron pressure cannot overcome gravity Big Bang, Black Massive Things: Galaxies, Stars and Black Holes104 Holes, No Math Topic 2: Stars • If the mass of the neutron star is so large that the gravity can overcome the neutron degeneracy that the core will Big Bang, Black Massive Things: Galaxies, Stars and Black Holes105 Holes, No Math Topic 2: Stars • This mass is about 3MSun • Stars with 1½ times the mass of the sun eventually can’t support itself against its own gravity and will collapse into a black-hole • Chandrasekhar limit Big Bang, Black Massive Things: Galaxies, Stars and Black Holes106 Holes, No Math Topic 2: Stars • Its as if we have a giant nucleus of neutrons only it’s held together by gravity not the strong force Big Bang, Black Massive Things: Galaxies, Stars and Black Holes107 Holes, No Math Topic 2: Stars • In some cases they may explode or manage to throw off enough matter to reduce their mass below the limit Big Bang, Black Massive Things: Galaxies, Stars and Black Holes108 Holes, No Math Topic 2: Stars TCP 17 cont… • (again p514) Big Bang, Black Massive Things: Galaxies, Stars and Black Holes109 Holes, No Math Topic 2: Stars Why is Iron Special? Need This • For the elements lighter than iron: every time you create a new, heavier nucleus, you release energy • For the elements heavier than iron: it takes energy to create them (don’t create light and doesn’t add to the heat of the star that keeps it from collapsing) • Thus, after all the atoms have turned into iron you can’t any more heat from crushing atoms together to form heavier atoms Big Bang, Black Massive Things: Galaxies, Stars and Black Holes110 Holes, No Math Topic 2: Stars TCP 17 cont… • Aside on neutron stars: • As neutron stars collapse they start spinning faster and faster (kinda like an ice skater pulling her arms in) • Picture from 218, chapter 10?11? • It emits light along its axis (picture on p527) • We see this beam of light as it sweeps past us. Kinda like a light house • Figure on p527 • Give these the creative name of pulsars Big Bang, Black Massive Things: Galaxies, Stars and Black Holes111 Holes, No Math Topic 2: Stars TCP 17 cont… • Actually we have found neutron stars that have planets orbiting them… kinda cool Big Bang, Black Massive Things: Galaxies, Stars and Black Holes112 Holes, No Math Topic 2: Stars • Weird stuff: more massive than the sun but just about 10 Km across, essentially a giant nuclei but different – Almost entirely neutrons (no protons) – Gravity, not the strong force, holds it all together Big Bang, Black Massive Things: Galaxies, Stars and Black Holes113 Holes, No Math Topic 2: Stars • If the mass of the star is one or two times the mass of the sun, the crush of gravity would be repelled by the exclusion principle between the neutrons and protons, rather than between the electrons Big Bang, Black Massive Things: Galaxies, Stars and Black Holes114 Holes, No Math Topic 2: Stars TCP 17 cont… • In the iron core (or if there is electron degeneracy) not really sure which, and the gravitational pressure continues then the electrons have enough energy such that that when they collide with protons they convert into a neutron and a neutrino • P511, Fig 16.16 (something better)?) • The iron core with a mass comparable to our Sun (is this the 1.4?) and once the electrons are gone, they don’t have the degeneracy pressure so gravity can start squeezing again making the electrons and protons more energetic so they convert into more neutrons until everything is just a just a bunch of neutrons • The neutrons also have a degeneracy that opposes the collapsing of gravity and our giant ball of iron that used to be the size of the earth collapses into a ball of neutrons just a few kilometers across • Its as if we have a giant nucleus Big Bang, Black Massive Things: Galaxies, Stars and Black Holes115 Holes, No Math Topic 2: Stars • Picture 17.2 (page 521) Big Bang, Black Massive Things: Galaxies, Stars and Black Holes116 Holes, No Math Topic 2: Stars • Pictures on p507 and 8 of TCP. Also 16.16 Big Bang, Black Massive Things: Galaxies, Stars and Black Holes117 Holes, No Math Topic 2: Stars The Birth of Stars • Gravity condenses hydrogen and helium into small clumps • Atoms get close enough that they start interacting with each other • As the atoms collide with one another we start to get nuclear reactions – “A Star is Born” Big Bang, Black Massive Things: Galaxies, Stars and Black Holes118 Holes, No Math Topic 2: Stars • Sometimes when a very massive star collapses, the outer regions may get blown off in a tremendous explosion called a supernovae • Results in a great cloud of hot shining dust blown out into space, spreading all the elements far and wide Big Bang, Black Massive Things: Galaxies, Stars and Black Holes119 Holes, No Math Topic 2: Stars • Pressure • TCP: Page 440, Fig S4.10 Big Bang, Black Massive Things: Galaxies, Stars and Black Holes120 Holes, No Math Topic 2: Stars – Supernovae – White Dwarf – Neutron Star – Black hole… – Pulsars – Worm holes? – MACHOS? – Red Giants? Big Bang, Black Massive Things: Galaxies, Stars and Black Holes121 Holes, No Math Topic 2: Stars • Another issue: Things speed up as they fall towards the center of the star: Just like a rock falling towards the earth speeds up brings energy into the star! Big Bang, Black Massive Things: Galaxies, Stars and Black Holes122 Holes, No Math Topic 2: Stars • This is a test… Big Bang, Black Massive Things: Galaxies, Stars and Black Holes123 Holes, No Math Topic 2: Stars • This is some text Big Bang, Black Massive Things: Galaxies, Stars and Black Holes124 Holes, No Math Topic 2: Stars Neutron Stars Big Bang, Black Massive Things: Galaxies, Stars and Black Holes125 Holes, No Math Topic 2: Stars • Nova video Big Bang, Black Massive Things: Galaxies, Stars and Black Holes126 Holes, No Math Topic 2: Stars • This is some text Big Bang, Black Massive Things: Galaxies, Stars and Black Holes127 Holes, No Math Topic 2: Stars • Don’t want to say too much here about the exclusion principle, eventually gravity can overcome the quantum mechanical effect of particles needing to not be in the same position/velocity state Big Bang, Black Massive Things: Galaxies, Stars and Black Holes128 Holes, No Math Topic 2: Stars Big Bang, Black Massive Things: Galaxies, Stars and Black Holes129 Holes, No Math Topic 2: Stars Big Bang, Black Massive Things: Galaxies, Stars and Black Holes130 Holes, No Math Topic 2: Stars Heat and pressure • As the atoms are drawn towards the center of the star they get faster (like a rock falling towards the surface of the earth) • As atoms combine in nuclear reactions they release energy and the atoms get more energetic • These higher energy atoms can try to escape the gravity of the star • Can think of this like a gas: If the atoms are getting more energetic we say they are being heated • As they atoms get more energetic (higher velocity) they can get further from the center of the star, again the same analogy as Big Bang, Black Massive Things: Galaxies, Stars and Black Holes131 throwing a rock from Topic the 2: surface of the earth Holes, No Math Stars • When the “gas” of energetic atoms gets heated its as if there is a “pressure” pushing the atoms away from the center like a balloon. If you heat up a balloon (or put more air in it) the atoms hit the walls of the balloon harder and we say it is under more pressure. What keeps the balloon together is the force that the plastic walls of the balloon exerts; what keeps the star together is the force of gravity pushing the atoms back towards the center of the star • We say that gravity exerts a “pressure” on atoms in the star • In a balloon, the inward pressure of the balloon walls balances the outward pressure of the gas. In a star gravity the pressure of gravity balances the outward pressure of the gas Big Bang, Black Massive Things: Galaxies, Stars and Black Holes132 Holes, No Math Topic 2: Stars • Probably want to finish the story about neutron stars and white dwarfs and such… That could also go into the next section… • Next some SHU 4 cont stuff.. Big Bang, Black Massive Things: Galaxies, Stars and Black Holes133 Holes, No Math Topic 2: Stars Stellar Cooking • The hydrogen effectively gets converted into helium and releases lots of energy in the form of photons, electrons and neutrinos • The heat released in this reaction, which is like a controlled hydrogen bomb explosion, is what makes a star shine • Raises the temperature of the star Big Bang, Black Massive Things: Galaxies, Stars and Black Holes134 Holes, No Math Topic 2: Stars SHU 4 • Probably want that astronomy book that did the different types of stars… Big Bang, Black Massive Things: Galaxies, Stars and Black Holes135 Holes, No Math Topic 2: Stars • After this fuel is spent the center can collapse into a very dense state such as a black hole… Are we getting into the next section? Big Bang, Black Massive Things: Galaxies, Stars and Black Holes136 Holes, No Math Topic 2: Stars Big Picture • The big picture about galaxy formation, stellar formation and a star’s life is the balance between the stuff that tries to compress it together and the stuff that keeps it from crushing itself into a tiny little thing. Big Bang, Black Massive Things: Galaxies, Stars and Black Holes137 Holes, No Math Topic 2: Stars Gravity • Let’s use the earth as an example. Let’s say I have a rock near the surface of the earth. That rock will fall to the surface of the earth. • Its been attracted • This is true for all objects near the earth. They fall towards the center of the earth Big Bang, Black Massive Things: Galaxies, Stars and Black Holes138 Holes, No Math Topic 2: Stars Other? • Ok… So all the things on the earth fall to the center of the earth… why doesn’t our rock fall to the center? Because it hits the ground. • So what?… what about the ground keeps it from falling to the center? I.e., what force OPPOSES gravity and keeps it from falling further? Why doesn’t the stuff already at the surface of the earth fall more? Why is the SURFACE of the earth not falling towards the center? Big Bang, Black Massive Things: Galaxies, Stars and Black Holes139 Holes, No Math Topic 2: Stars Opposition • The reason it doesn’t fall towards the center of the earth is that the “stuff” of the ground “pushes back” • How does it push back? • The atoms of the stuff that make up the earths surface are bound together (this is chemistry in some real sense) • For the rock to “pass through” the surface would mean having to break the bonds that hold the atoms together • These bonds can be VERY strong • The bonds in the atoms of paper are much weaker than the bonds of steel Big Bang, Black Massive Things: Galaxies, Stars and Black Holes140 Holes, No Math Topic 2: Stars Summary • So… The surface of the earth is where it is because gravity is pushing it towards the center, but the stuff below the surface is “pushing back” since the push of gravity isn’t strong enough to break the bonds of the stuff below it • If the bonds weren’t strong (but did exist) like in water, if the rock hit water it would fall through the water until it hit something it couldn’t fall through. • Bottom line: What’s important is that gravity causes things to compress and some other force keeps things from compressing Big Bang, Black Massive Things: Galaxies, Stars and Black Holes141 Holes, No Math Topic 2: Stars Galaxy Formation (BHOT 8 continued) • Galaxy formation: • After the big bang we just had lots of stuff floating around in space • Can think of this as just being a giant tank of gas. • After a few million years the electromagnetic attractions (electrons to nuclei) would start forming atoms (already said this) Big Bang, Black Massive Things: Galaxies, Stars and Black Holes142 Holes, No Math Topic 2: Stars • The gravitational attraction would eventually stop expansion in some regions and start them to collapse • As they were collapsing, the gravitational pull of matter outside these regions might start them rotation slightly • As the collapsed region got smaller, it would spin faster– just like ice skaters spin faster on ice as they draw in their arms. • Eventually, when the region got small enough it would be spinning fast enough to balance the attraction of gravity to balance the attraction of gravity and in this way, we believe, disk-like rotating galaxies were born Others would form other times of galaxies like elliptical galaxies. • In this manner the clouds coalesce into starts like our sun, burning hydrogen into helium and radiating the resulting energy as heat and light Big Bang, Black Massive Things: Galaxies, Stars and Black Holes143 Holes, No Math Topic 2: Stars Star Formation (TOE 3… BHOT 8 cont…) • As time went on the hydrogen and helium gas in the galaxy would condense under their own gravity • This would create proto-stars. Read: effectively a ball of gas in space, just concentrated in one area because of the gravitational attraction • As these contracted (again by gravity), the atoms would collide with one another • As things fell to the “center” their speed would increase (like a ball falling to the surface of the earth picks up speed) the temperature would increase until eventually it became hot enough (particles are energetic enough) to start nuclear fusion reactions (i.e., when they collide) • Picture of a fusion reaction that converts hydrogen into helium and releases a lot of light (photons) Big Bang, Black Massive Things: Galaxies, Stars and Black Holes144 Holes, No Math Topic 2: Stars • These would convert the hydrogen to make more helium. The heat released in this reaction, which is like a controlled hydrogen bomb explosion, is what makes a star shine. • Pictures on p507 and 8 of TCP. Also 16.16 Big Bang, Black Massive Things: Galaxies, Stars and Black Holes145 Holes, No Math Topic 2: Stars Star Formation (BHOT 8 cont… TOE 3) • This additional heat also increases the pressure of the gas until it is sufficient to balance the gravitational attraction and the gas stops contracting • In this manner the clouds coalesce into starts like our sun, burning hydrogen into helium and radiating the resulting energy as heat and light • This can stay stable for billions of years Big Bang, Black Massive Things: Galaxies, Stars and Black Holes146 Holes, No Math Topic 2: Stars BHOT 8 cont… • Our star: Can last for another 5 billion years or so • Others can last as little as a hundred million years Big Bang, Black Massive Things: Galaxies, Stars and Black Holes147 Holes, No Math Topic 2: Stars BHOT 8 cont… • What happens when the star starts to run out of fuel? • Since there isn’t enough hydrogen around to keep making helium at a fast enough rate, the heat can’t keep the gravity off any more and the star starts to contract (i.e., get smaller) • This causes the atoms closer together and the star gets hotter again and we burn even the remaining hydrogen • What happens when the hydrogen is all gone and all we have left is the helium produced from fusion? Big Bang, Black Massive Things: Galaxies, Stars and Black Holes148 Holes, No Math Topic 2: Stars • Instead of converting hydrogen to helium (because there isn’t much hydrogen left), the helium starts interacting (again chemistry) and gets converted into heavier elements like carbon and oxygen (this is where the carbon and oxygen in the universe comes from). Need a picture here • After this fuel is spent the center can collapse into a very dense state (white dwarf, neutron star or a black hole) Big Bang, Black Massive Things: Galaxies, Stars and Black Holes149 Holes, No Math Topic 2: Stars TCP 17 • Do we have enough on stellar formation? • The afterworld of stars: White dwarfs, neutron stars and black holes Big Bang, Black Massive Things: Galaxies, Stars and Black Holes150 Holes, No Math Topic 2: Stars • Paradoxically: the more fuel a star starts off with the sooner it runs out. This is because the more massive the star is the hotter it needs to be to balance its gravitational attraction. And the hotter the star the faster the nuclear reactions occur and the sooner it will use its fuel • Important point: Because the strength of the force of gravity depends on the mass of the star (and so in effect on its size and weight) the star’s fate depends on its size Big Bang, Black Massive Things: Galaxies, Stars and Black Holes151 Holes, No Math Topic 2: Stars • Then the star life cycle starts and the hydrogen burns and turns into helium • As the hydrogen gets used up gravitational pressure increases and the helium starts to fuse • One by one the heavier elements are produced, each in turn fueling reactions to produce the heaviest element as gravity compresses the star into a denser and denser mass Big Bang, Black Massive Things: Galaxies, Stars and Black Holes152 Holes, No Math Topic 2: Stars TCP 17 cont… • The battle between the “crush” of gravity and the outward pressure of the nuclear burning that governs a star’s life • Here we talk about what happens as that fuel begins to run out Big Bang, Black Massive Things: Galaxies, Stars and Black Holes153 Holes, No Math Topic 2: Stars TCP 17 cont… • Start with small stars (kinda did this already), like our sun • After all the nuclear burning all we are left with is the products of the burning • Typically this is carbon • Slightly bigger ones will be able to crate iron Big Bang, Black Massive Things: Galaxies, Stars and Black Holes154 Holes, No Math Topic 2: Stars • Since it happens in roughly the same way, they all look the same • Since we measure the amount of light we can tell how far away it occurred • This is pretty damn cool! Big Bang, Black Massive Things: Galaxies, Stars and Black Holes155 Holes, No Math Topic 2: Stars TCP 17 cont… • Theoretical calculations show that a white dwarf cannot be larger, in mass, 1.4 Sun • This is the Chandrasekar limit • At this mass the compression is so big that the electrons get so fast that they approach the speed of light • Unfortunately, they can’t get any fasters than light so the game breaks down Big Bang, Black Massive Things: Galaxies, Stars and Black Holes156 Holes, No Math Topic 2: Stars TCP 17 cont… • After 1.4 MSun gravity is stronger than the electron degeneracy pressure and the star collapses further, heating the star until the temperature is big enough for carbon fusion • The star explodes in a White Dwarf Supernova • Not sure how this ends… Big Bang, Black Massive Things: Galaxies, Stars and Black Holes157 Holes, No Math Topic 2: Stars • • Mention the difference between massive star supernovae and the “carbon bomb” white dwarf supernovae White dwarf supernovae are especially cool because they always happen when the WD reaches the critical mass of 1.4MSun when you get the carbon bomb stuff and the thing explodes (we call this a type 1a supernova) Big Bang, Black Massive Things: Galaxies, Stars and Black Holes158 Holes, No Math Topic 2: Stars Death of White Dwarf’s • Depending on its size, once iron is formed in the star, it either dies slowly and sheds its elements into space – Why does it sped its elements into space? Big Bang, Black Massive Things: Galaxies, Stars and Black Holes159 Holes, No Math Topic 2: Stars Stuff on Electron Degeneracy • Do we want an aside about degeneracy? • Since there is no burning to counteract the gravity it shrinks until the electrons get so close together that, for quantum mechanical reasons, they can’t get any closer (electron degeneracy) • A white dwarf is supported by the exclusion principle repulsion between electrons in the matter Big Bang, Black Massive Things: Galaxies, Stars and Black Holes160 Holes, No Math Topic 2: Stars TCP 16 and 17 Continued • This incredible compression releases a huge amount of energy and is what we call a supernova • (It can shine so brightly that it looks like about 10 billion suns for about a week) • Page 114 Big Bang, Black Massive Things: Galaxies, Stars and Black Holes161 Holes, No Math Topic 2: Stars