Lecture notes on supernova, Oct 22

Most stars are pretty stable for most of their lifetimes.

ex:  the sun (30% brighter now b/c of inert He core, but otherwise same as 
	4x10^9 years ago)

Main sequence pretty much the same for all stars 
	-- burning hydrogen
	-- shorter life for massive stars than low-mass stars

It's stellar death that's very different for different stars!

We're going to talk about how stars die.  Some die by fire, some by ice.
	
Already talked about death by ice = cooling white dwarf, the sun's fate.

Certain stars blow up.  (The sun will NOT blow up!!)
	A star blowing up makes an explosion brighter than the whole 
galaxy!
	Many explosions all at once can disrupt small galaxies!
	Extreme conditions (very hot, very fast, very violent)
	Explosion creates many of the heavy metals you know and love. 

YOU ARE STAR-STUFF.  Most of the elements in your body were created in 
the cores of now-dead stars, then cast away by stellar winds or violently 
ejected when the star blows, then drifted through space to a gas cloud, 
and accreted to become the earth when the sun formed.   You are 
star-stuff:
Think about that.

How did the elements get made?
	In the last 50 years, this question's been largely answered!
	H and He formed about 3 minutes after the Big Bang.
	Sun makes C (carbon), O (oxygen), N (nitrogen), but not heavy 
elements.
	Explosions of stars create most of the rest.

For example, consider:
	the hydrogen holding your DNA helix together - formed in Big Bang.
	the calcium your bones are made of - from explosive fusing of 
oxygen
		in a supernova
	the iron carrying oxygen through your body- from explosive burning
		of silicon, in the supernova, further toward the core 
	the gold in your ring - nuclei gorging on neutrons in the 
supernova.
We'll talk more about how this happens.

(Aside)
fuse carbon in a supernova, make:  Ne, Mg, Al, Na, Si
fuse oxygen in a supernova, make:  Si, S, Ar, Ca
fuse silicon in a supernova, make: Fe and similar-mass elements
rapid force-feeding of neutrons by nuclei, make: Pb, Au, Uranium
(end aside)



Historical supernova:
July 4, 1054 AD, Chinese astronomers noted a "Guest Star" in Taurus.
	(Chinese recorded about 75 novae and supernovae, in total)
	brighter than the brightest planet
	visible in daytime for weeks
	visible to the naked eye in China for 653 days
	also noted by Anasazi in Chaco Canyon and Arizona; Japanese, 
Arabs?
	now the Crab Supernova remnant
	
Motivating questions:
	What are the fates of stars?
	What kinds of stars explode?
	Why, if stars are stable for millions of years, do some suddenly 
blow up?
	What's the connection between SNe and neutron stars and black 
holes?
	What elements are alchemized in supernovae?  How?

what's in a name?
	- novae are thermonuclear burps on white dwarfs
	- supernova are exploding stars.  completely different phenomenon 
from novae!
	- but look similar to naked-eye observer
	- "nova" is Latin for "new", because a nova looks like a new star 
in the sky

What data do we have?
	we can see the explosions (measure spectra and brightness vs. 
time)
	fireball left over after the explosion -- renmants
	We looked at lots of pretty pictures 
(http://satchmo.as.arizona.edu/~jrigby/sne.html)


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