1. Outline ● Novae (detonations on the surface of a star) ● Supernovae (detonations of a star) ● The Mystery of Gamma Ray Bursts (GRBs) ● Sifting through afterglows for clues

2. Stellar Explosions Novae White dwarf in close binary system WD's tidal force stretches out companion, until parts of outer envelope spill onto WD. Surface gets hotter and denser. Eventually, a burst of fusion. Binary brightens by 10'000's! Some gas expelled into space. Whole cycle may repeat every few decades => recurrent novae.

3. Nova V838Mon with Hubble, May – Dec 2002 4.2 pc

4. Death of a High-Mass Star M > 8 M Sun Iron core Iron fusion doesn't produce energy (actually requires energy) => core collapses in < 1 sec. Ejection speeds 1000's to 10,000's of km/sec! (see DEMO) Remnant is a “neutron star” or “black hole”. T ~ 10 10 K, radiation disrupts nuclei, p + e => n + neutrino Collapses until neutrons come into contact. Rebounds outward, violent shock ejects rest of star => A Core-collapse or Type II Supernova Such supernovae occur roughly every 50 years in Milky Way.

5. Binding Energy per nucleon

6. Example Supernova: 1998bw

7. Cassiopeia A: Supernova Remnant

8. A Carbon-Detonation or “Type Ia” Supernova Despite novae, mass continues to build up on White Dwarf. If mass grows to 1.4 M Sun (the "Chandrasekhar limit"), gravity overwhelms the Pauli exclusion pressure supporting the WD, so it contracts and heats up. This starts carbon fusion everywhere at once. Tremendous energy makes star explode. No core remnant.

9. Supernova 1987A in the Large Magellanic Cloud

10. 1994 1998 Expanding debris from star. Speed almost 3000 km/sec! Light from supernova hitting ring of gas, probably a shell from earlier mass loss event. SN 1987A is evolving fast!

11. A Young Supernova SN 1993J Rupen et al.

12. In 1000 years, the exploded debris might look something like this: Crab Nebula: debris from a stellar explosion observed in 1054 AD. Vela Nebula: debris from a stellar explosion in about 9000 BC. Or in 10,000 years: 2 pc 50 pc

13. Remember, core collapse (Type II) and carbon-detonation (Type I) supernovae have very different origins

14. Supernova light curves

15. Making the Elements Universe initially all H (p’s and e’s). Some He made soon after Big Bang before stars, galaxies formed. All the rest made in stars, and returned to ISM by supernovae. Elements up to iron ( 56 Fe, 26 p + 30 n in nucleus) produced by steady fusion (less abundant elements we didn’t discuss, like Cl, Na, made in reactions that aren’t important energy makers). Solar System formed from such "enriched" gas 4.6 billion years ago. As Milky Way ages, the abundances of elements compared to H in gas and new stars are increasing due to fusion and supernovae. Heavier elements (such as lead, gold, copper, silver, etc.) by "neutron capture" in core, even heavier ones (uranium, plutonium, etc.) in supernova itself.

16. Clicker Question: What is the remnant left over from a Type Ia (carbon detonation) supernova? A: a white dwarf + expanding shell B: a neutron star + expanding shell C: a black hole + expanding shell D: no remnant, just the expanding shell

17. Clicker Question: What is the heaviest element produced by stellar nucleosynthesis in the core of a massive star? A: Hydrogen B: Carbon C: Iron D: Uranium

18. Clicker Question: All of the following atoms have a total of 4 nucleons (protons or neutrons). Which of the following has the smallest mass? A: 4 hydrogen atoms B: 2 deuterium atoms C: 1 tritium atom and 1 hydrogen atom D: 1 Helium atom E: None of the above, they all have the same total mass

19. 1. White Dwarf If initial star mass < 8 M Sun or so. (and remember: Maximum WD mass is 1.4 M Sun, radius is about that of the Earth) 2. Neutron Star If initial mass > 8 M Sun and < 25 M Sun. 3. Black Hole If initial mass > 25 M Sun. Final States of a Star

20. Pulsars Discovery of LGM1 by Jocelyn Bell and Tony Hewish (Cambridge) in 1967. Nobel Prize to Hewish in 1974. Pulse periods observed from 0.001 sec to 10 seconds - DEMO Explanation: "beamed" radiation from rapidly spinning neutron star. Usually neutron stars are pulsars for 10 7 years after supernova.

21. The Crab Pulsar

22. Neutron Stars Leftover core from Type II supernova - a tightly packed ball of neutrons. Diameter: 20 km only! Mass: 1.4 - 3(?) M Sun Density: 10 14 g / cm 3 ! Surface gravity: 10 12 higher Escape velocity: 0.6c Rotation rate: few to many times per second!!! Magnetic field: 10 12 x Earth's! A neutron star over the Sandias?

23. An Isolated Neutron Star T ~ 2 million K Size ~ 30 km

24. The Lighthouse model of a pulsar

25. Pulsars are incredibly accurate clocks! Example: period of the first discovered "millisecond pulsar" is: P = 0.00155780644887275 sec It is slowing down at a rate of 1.051054 x 10 -19 sec/sec The slowing-down rate is slowing down at a rate of: 0.98 x 10 -31 /sec

26. Multi-wavelength observations of Pulsars

27. Pulsar Exotica Binary pulsars: two pulsars in orbit around each other. Einstein predicted that binary orbits should "decay", i.e. the masses would spiral in towards each other, losing energy through "gravitational radiation". Confirmed by binary pulsar. year Curve: prediction of decaying orbit. Points: measurements. Planets around pulsars: A pulsar was found in 1992 to have three planets! Masses about 3 M Earth, 1 M Earth, and 1 M Moon ! Millisecond pulsars: periods of 1 to a few msec. Probably accreted matter from a binary companion that made it spin faster. Gamma-ray Bursts: some pulsars produce bursts of gamma-rays, called Soft Gamma-Ray Repeaters or SGRs

28. Time history of the 4 confirmed SGRs: Woods & Thompson 2004

29. Soft Gamma-Ray Repeaters X-ray image " E iso ~ a few10 44 erg in gamma-rays Where does this energy come from? - Accretion? No sign of a disk - Rotation? Not enough energy available - Magnetic fields? Yes

30. Clicker Question: What is our basic model for a pulsar? A: a rotating white dwarf B: a rotating neutron star C: a rotating black hole D: an oscillating star

31. Clicker Question: What is the diameter of a 2 M sun neutron star? A: 20 km B: 2000 km C: 14,000 km (size of the Earth) D: 1,400,000 km (size of the Sun)

32. Vela satellite An early gamma ray-burst

33. A Gamma Ray Burst Sampler

34. Great debate: 1967-1997

35. GRBM: 40-600 keV WFC: 2-30 keV NFI: 2-10 keV Bepposax Satellite

36. X-Ray Afterglow from GRB 971214 t=6.5 hrst=12.5 hrst=54 hrs