1. The Deaths of Stars Please press “1” to test your transmitter

2. The Final Breaths of Sun-Like Stars: Planetary Nebulae The Helix Nebula Remnants of stars with ~ 1 – a few M sun Radii: R ~ 0.2 - 3 light years Expanding at ~10 – 20 km/s (← Doppler shifts) Less than 10,000 years old

3. The Formation of Planetary Nebulae Two-stage process: Slow wind from a red giant blows away cool, outer layers of the star Fast wind from hot, inner layers of the star overtakes the slow wind and excites it => Planetary Nebula

5. The Dumbbell Nebula in Hydrogen and Oxygen Line Emission

6. Planetary Nebulae Often asymmetric, possibly due toasymmetric Stellar rotation Magnetic fields Dust disks around the stars The Butterfly Nebula

7. A sun-like star is building up elements through nuclear fusion up to which element(s)? 1.Hydrogen 2.Helium 3.Carbon and Oxygen 4.Iron 5.Uranium

8. The Remnants of Sun-Like Stars: White Dwarfs Carbon-Oxygen (C,O) core does not ignite Carbon fusion. He-burning shell keeps dumping C and O onto the core. C,O core collapses until gravity is balanced by pressure from a new state of matter: Degenerate Matter

9. White Dwarfs Degenerate stellar remnant (C,O core) Extremely dense: 1 teaspoon of WD material: mass ≈ 16 tons!!! White Dwarfs: Mass ~ M sun Temp. ~ 25,000 K Luminosity ~ 0.01 L sun Chunk of WD material the size of a beach ball would outweigh an ocean liner!

10. Considering the luminosity (0.01 L sun ) and surface tempmerature (25,000 K) of a white dwarf, where do you expect to find white dwarfs in the Hertzsprung-Russell diagram? 1.In the upper left corner 2.In the lower left corner. 3.In the lower right corner. 4.In the upper right corner. 5.In the center. 1 5 4 3 2

12. White Dwarfs in Binary Systems Binary consisting of WD + MS or Red Giant star => WD accretes matter from the companion Angular momentum conservation => accreted matter forms a disk, called accretion disk. Matter in the accretion disk heats up to ~ 1 million K T ~ 10 6 K

13. Considering that material in the accretion disk around a white dwarf heats up to ~ 1 million o K, in which wavelength band do you expect that it radiates the most strongly? 1.Infrared 2.Optical 3.Ultraviolet 4.X-rays 5.Gamma-rays

14. White Dwarfs in Binary Systems Binary consisting of WD + MS or Red Giant star => WD accretes matter from the companion Angular momentum conservation => accreted matter forms a disk, called accretion disk. Matter in the accretion disk heats up to ~ 1 million K T ~ 10 6 K X-ray emission => X-ray emission => “X-ray binary”.

15. Nova Explosions Nova Cygni 1975 Hydrogen accreted through the accretion disk accumulates on the surface of the WD  Very hot, dense layer of non- fusing hydrogen on the WD surface  Explosive onset of H fusion  Nova explosion In many cases: Cycle of repeating explosions every few years – decades.

16. A very massive (> 8 M sun ) star is building up elements through nuclear fusion up to which element(s)? 1.Hydrogen 2.Helium 3.Carbon and Oxygen 4.Iron 5.Uranium

17. The Deaths of Massive Stars: Supernovae The Crab Nebula Final stages of fusion in high- mass stars (> 8 M sun ), leading to the formation of an Iron core, happen extremely rapidly: Si burning lasts only for ~ 1 day. Iron core ultimately collapses, triggering an explosion that destroys the star: A Supernova

18. The Deaths of Massive Stars: Supernovae

19. Do you think a supernova is bright enough to see it in a distant galaxy? 1.No, only out to a few hundred light years, i.e., in the neighborhood of our Sun, within our Milky Way. 2.No, not in other galaxies, but throughout our Milky Way. 3.Yes, but only nearby galaxies in our Local Group. 4.Yes, out to about half the distance through the visible Universe. 5.Yes essentially throughout the entire visible Universe.

20. Supernovae Energy released in a Supernova: 10,000,000,000,000,000,000,000,000 (10 25 ) times the energy of a Hydrogen bomb! Luminosity of a Supernova: 10,000,000,000 (10 10 ) times the power output of the sun! Comparable to the power of an entire galaxy

21. Supernova in a distant galaxy

22. The Famous Supernova of 1987: SN 1987A BeforeAt maximum Unusual Supernova in the Large Magellanic Cloud in Feb. 1987

23. The Remnant of SN 1987A Ring due to SN ejecta catching up with pre- SN stellar wind; also observable in X-rays.X-rays

24. Supernova Remnants The Cygnus Loop The Veil Nebula The Crab Nebula: Remnant of a supernova observed in a.d. 1054 Cassiopeia A Optical X-rays

25. A different kind of Supernova: Type Ia Supernovae White Dwarf in a binary system accreting matter from a companion star. Untill it becomes too massive to be a White Dwarf  Collapse!  Supernova

26. Type Ia Supernovae

27. Alternative Scenario: Merger of two white dwarfs