1. Supernovae

2. An extremely rare endpoint
Most stars either have M < 1.4 Mʘ, or can lose enough mass during post-main sequence evolution to get there, and end as white dwarf
However if core is more massive, nothing can stop gravitational collapse
The final stages take just seconds, and result in a massive fusion explosion

3. How rare is “rare?”
There has not been one in our Galaxy since the invention of the telescope 400 years ago!
They are so bright that we can easily see them in other galaxies, and estimate how often they go off
A typical galaxy of 200 x 109 stars has only one SN every 100 years!
If they are so rare, how do we know this rate? Do we need to watch for 100 years?

5. How “super” is a supernova: the “light curve”
At maximum brightness, for about a week or two the SN can reach the same luminosity as the sum of all the 1011 stars in the entire host galaxy!

6. Our Milky Way Galaxy is “overdue” for a supernova
Last local SN was more than 400 years ago (1604) [so, maybe soon!]
Johannes
Kepler

7. Our Milky Way Galaxy is “overdue” for a supernova
Last local SN was 400 years ago
However, in 1987 one occurred in our nearest neighbor galaxy, the Large Magellanic Cloud, 180,000 lt-yr away

8. Supernova “1987a” in LMC

9. Supernova “1987a” in LMC

11. Want to bet on the next Milky Way supernova?
I’d put my money on η Carinae

13. There are actually two different paths that can lead to a supernova
The collapse of a massive star – “Type II”
Mass exchange on to a white dwarf in a binary system --- “Type I”
Most stars are actually in binary systems – our Sun happens to be an exception

14. If the two stars in a binary orbit are sufficiently close, “mass exchange” can occur
Process is slow, perhaps 10-8 Mʘ /yr
But in 108 yr, that means 1 Mʘ of stuff piles up on the white dwarf, which often had an initial mass of 0.4 Mʘ
Recall, electron pressure can only support 1.4 Mʘ
Then what??

15. Why are supernova important?
All the elements more complex than iron are formed!

16. SN as “standard candles”
A certain subclass of Type I supernova turn out to all have the same
luminosity when they are at their brightest

17. SN and Gamma Ray Bursts

18. A secret during the Cold War: the “Vela” Satellites

19. A Cold War Secret: Gamma Ray Burst (“GRB”)

21. Thousands of GRBs are now known
But, are they nearby (relatively little energy released), or very far away (large energy release)?

22. Thirty years later
GRBs prove to lie inside of very distant galaxies)

23. Now that we know the distance to each GRB event, we can calculate the energy (luminosity) generated in each burst
There are roughly 1011 stars in a typical galaxy
There are roughly 1010 galaxies within range of the largest
telescopes
For the few second that a GRB is in progress, that single event generates more energy than the sum of every star in every galaxy in the entire observable Universe, all 1021 stars!

24. Do all supernovae make Gamma Ray bursts? No
Why do some make GRBs, but others not?

25. Discovery of new supernovae

27. Discovery of a new
Gamma Ray Burst
Swift Satellite

29. Stuff Supernovae leave behind

30. Stuff Supernovae leave behind

31. Stuff Supernovae leave behind

32. Doppler Effect: motion between source of a wave and the observer slightly changes the wavelength