1. Announcements Exam 3 is scheduled for Wednesday April 8. Will be pushed back to Monday April 13 Tentatively will cover the rest of Chapter 4, all of Chapters 5 & 6 and some of Chapter 7 (will now how much next week). Sample Questions are posted. 1 st Quarter Observing Night tomorrow night. Set-up starts at 6:30 if clear, 6:45 if cloudy. Meet outside B-310

2. Type II Supernova: Death of a massive star Photodisintegration Fe +  He Reverse Beta Decay e - + p + n +

3. Other Types of Supernovae

4. Type Ia: White Dwarf Explosion When a white dwarf exceeds the Chandrasekhar limit of 1.2 M sun, it detonates in a Type Ia supernova. The spectrum has no hydrogen lines but lots of silicon and iron. The white dwarf star is completely destroyed.

5. Type Ib: Stripped Supergiant If a massive star has its outer layers stripped off, perhaps by previous eruptions or a companion, it will be a blue supergiant when it dies. No hydrogen in the spectrum but lots of helium.

6. Type Ic: Naked Supergiant If even the helium has been stripped off, there will be only heavier elements in the spectrum

7. The Light Curve of the various types is also different

8. The progenitor for each supernova type is different Type Ia White Dwarf detonation Core Collapse

9. What is left after a supernova? A supernova remnant is only visible for a few thousand years before it fades from view.

10. Pulsars: LGM? Jocelyn Bell and Antony Hewish discovered extremely regular radio pulses coming from an object in Vulpecula

11. Pulsars are spinning Neutron Stars The Lighthouse Model

13. The Crab pulses in all wavelengths

14. What causes emission in all wavelengths? Synchrotron Radiation

15. The Heart of the Crab Nebula Intense “winds” blowing away from the equator of the pulsar create a disk of swirling material around the pulsar. Jets can also be seen emanating from the poles of the pulsar. Watch Crab Pulsar video

16. If a pulsar is radiating energy, where is it coming from?

17. Pulsar Spin-down and Glitches An SGR is a Soft Gamma ray Repeater. They have magnetic fields thousand of times more intense than normal neutron stars. Normal neutron stars can also show sudden changes in their rotational periods

18. Internal Structure of a Neutron Star At the very center may be a core of strange matter: matter composed of a “fluid” of strange quarks

19. When a glitch occurs on a magnetar, a blast of gamma rays is emitted Watch Magnetar Flare video

20. Pulsars in binary systems can be extremely active

21. Millisecond Pulsars Watch Millisecond Pulsar video

22. Even More Bizarre: Binary Pulsars Watch Binary Pulsar, Formation of Binary Pulsar and Colliding Neutron Stars video

23. Is there a limit to mass of a neutron star? ~2 – 3 M sun

24. Hypernova What if the iron core is more than 3 solar masses?

25. Black Holes and relativity Newtonian physics won’t work here. We need new physics

26. What is meant by “the Universe”? Must distinguish between “the universe” and “the visible universe” The Universe…all things physical and all things which can influence the physical: matter, energy, space-time The Visible Universe…that part of the universe which we can see from Earth: a sphere with a radius of about 13.8 Gly

27. Are space & time part of the universe? According to Newton space and time are absolute and separate and are what the universe exists in. According to Einstein space-time interacts with and influences the physical so it is part of the universe

28. If space and time are part of the universe then there was no “before” the universe nor did the universe expand into empty space

29. The Anthropic Principle What is our relationship with the universe?

30. The Weak Anthropic Principle

31. The Strong Anthropic Principle Gives humanity an important “position” in the universe. Without us the universe would not exist.

32. The Cosmological Principle

33. Isotropic at the center but not homogeneous

34. Homogeneous but not isotropic

35. Isotropic and homogeneous

36. Our universe is obviously not homogeneous or isotropic close by