Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr. David Toback Lecture 21 & 22

1. Big Bang, Black Holes, No MathASTR/PHYS 109Dr. David TobackLecture 21 & 22

2. Was due Today – L22 • Reading: • Unit 5 (already due) • 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 before class

3. Unit 5: Big Objects • Galaxies • Star Birth and Death • 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

4. Important Buzz Words Wanted to make sure we had a lecture where we explained some of the important buzz words in astronomy: • Red Giants • Supernovae • White Dwarfs • Neutron Stars • Black Holes

5. 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

6. Where are we now in the history? A few hundred million years after the bang, stars start forming

7. 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

8. 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

9. Star Formation • This is some text..

10. Step 2 • More…

11. Step 3 • This is some text… Beginnings of planets!

12. Stars have some things in common with Spiral Galaxies Will be the star Will be the planets Gee… kinda looks like Saturn also…

13. Describing Stars We tend to use metaphors to describe Stars • Can think of them like people: They have a birth, a life and a death • Can think of them like a car: They run on “fuel,” and “die” when they run out of fuel • Can think of them like a balloon: A giant collection of atoms that are “forced” to stay inside the balloon walls

14. 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

15. Low energy (temperature) hydrogen reactions Proton Electro-magnitism Reaction Same charges repel Proton=Hydrogen Proton

16. 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

17. 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 Out-going particles get LOTS of energy Proton

18. The Life and Death of Stars A star’s life is effectively a battle between: • Gravity trying to crush everything into a tiny point • The nuclear interactions “opposing” the gravity

19. 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

20. 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

21. Hydrogen Reactions • Proton + Proton • Deuterium + Electron + Neutrino Proton Anti-Electron Nuclear Reaction Deuterium Proton=Hydrogen Neutrino Fusion produces particles with LOTS of energy Proton

22. Hydrogen and Deuterium Proton + Deuterium  3He + Photon Again, lots of energy to the particles Deuterium Photon Nuclear Reaction 3He Proton

23. Creating Stable Helium 3He + 3He  4He + 2 Hydrogens More energy is released 3He Hydrogen Nuclear Reaction 4He Hydrogen 3He

24. 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?

25. 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

26. Small speed objects can’t leave the Earth Look at the different things that can happen at various speeds on various size “heavenly bodies”

27. Another example with the same speed bullet but on the Moon

28. If we move to an asteroid, then it CAN leave

29. Can build things that shoot fast enough to leave the Moon

30. 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

31. 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

32. 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 • Can stay stable for billions of years Gravity Nuclear Reactions

33. The Fuel of a Star The Hydrogen and Helium provide the “fuel” that both: • Creates the light we see • Keeps the star stable Converts light atoms into heavy atoms

34. 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 fuel?

35. 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

36. 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, and complicated things can happen

37. 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 helium into Carbon

38. 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”

39. 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

40. 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, it takes so long for this to happen that none have been observed

41. Next move to heavier stars…

42. The Life of a Star Continued… • If the star is massive enough, the core can get to a temperature of 100 million Kelvin, and helium fusion can start • Helium can fuse to make heavier elements

43. Stages in a Massive Star’s Life

44. Converting Helium to Beryllium 4He 4He4 + 4He4  8Beryllium Nuclear Reaction 8Beryllium 4He

45. Converting Beryllium to Carbon 8Beryllium + 4He  12Carbon + Photon 8Beryllium 12Carbon Nuclear Reaction Photon 4He

46. 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

47. 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

48. 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 can REALLY crush the star

49. 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

50. Creating Neutron Stars Proton + Electron  Neutron + Neutrino Electron Neutrino(leaves the star) Up Quark Down Quark Down Quark Up Quark Proton Neutron