1. Life Cycles of Stars

2. The Hertzsprung-Russell Diagram

3. How Stars Form Collapsing gas and dust cloud
Protostar - mostly infrared

4. Main Sequence Stars Brown Dwarf (L, T, Y) Red Dwarf (M)
Normal Star (O, B, A, F, G, K)

5. All Objects Exist Because of a Balance Between Gravity and Some Other Force
People, Planets-Interatomic Forces
Normal Stars-Radiation
White Dwarfs-Electron Repulsion
Neutron Stars-Nuclear Forces
Quark Stars?
Black Holes-No Known Force

6. Mass, Luminosity, Lifetime
Luminosity = Mass3.5 (Solar Units)
Lifetime = Mass/Luminosity = 1/Mass2.5
Mass = .1: Lifetime = 316 (3160 b.y.)
Mass = .5: Lifetime = 5.7 (57 b.y.)
Mass = 1: Lifetime = 1 (10 b.y.)
Mass = 10: Lifetime = .003 (3 m.y)
Mass = 50: Lifetime = (570,000 yr)

7. Mass, Luminosity, Lifetime

8. Before Stars Form Pre-stellar cores Protostars
Pre-main sequence star (PMS)
Planet system formation. 

9. Protostars or Young Stellar Objects (YSO’s)
Class 0 (T <70K) Emits in microwave range because of opaque surrounding cloud
Class I (T = K) Emits in infrared. Star still invisible but can detect warm material around it.
Class II (T = K) T Tauri stars. Massive expulsion of material       
Class III(T > 2880K) PMS stars

10. Early Stars and Planets
(Class 0) Early main accretion phase
(Class I) Late accretion phase
(Class II) PMS stars with protoplanetary disks
(Class III) PMS stars with debris disks

11. Super-Massive Stars
Stars beyond a certain limit radiate so much that they expel their outer layers
W stars (Wolf-Rayet stars) are doing this: T Tauri on steroids
Upper limit about 100 solar masses
More massive stars can form by merger but don’t last long

12. Wolf-Rayet Star

13. How Stars Die Main Sequence Stars Brighten With Age
The More Massive a Star, the Faster it Uses Fuel
Giant Phase
White Dwarf
Supernova
Neutron Star - Pulsar
Black Hole

14. Leaving the Main Sequence
Helium accumulates in core of star
Fusion shuts down
Star begins to contract under gravity
Core becomes denser and hotter
Nuclear fusion resumes around helium core
Outer layers puff up enormously but cool down
Star becomes redder and larger (Red Giant)

15. “Live hard, die young, leave a good looking corpse”

16. Peeling off to the Giant Phase

17. Later Lives of Giants
Inert helium core begins to fuse helium to carbon and oxygen
Contraction of core stops
Outer envelope contracts and heats up
Red Giant becomes Yellow Giant
Helium core runs out of fuel
Helium fusion shell on outside of core, hydrogen fusion above
Star loops between red and yellow on H-R plot

18. Making the Elements Heavy nuclei: Energy from Fission
Light Nuclei: Energy from Fusion
Both end at Iron: Most stable nucleus
Stars can generate H-Fe through Fusion
How do we get beyond Fe?
Two processes
S-Process (Slow) in Red Giants
R-Process (Rapid!) in Supernovae

19. Beyond Helium He + particle = mass 5: not stable
He + He = Mass 8: Not Stable
The Mass 5-8 Bottleneck
Sometimes three He collide to make C
Li, Be, B rare in Universe
Destroyed in Stars
Created by spallation - knocking pieces off heavier atoms

20. Iron and Beyond
Build from C to Fe by fusing successively heavier atoms
Can’t Build Beyond Fe by Adding Protons
Repulsion of nuclei = Charge1 x Charge2
He + C = O: Repulsion = 2 x 6 = 12
Fe + p = Co: Repulsion = 26 x 1 = 26
Can Add Neutrons Until Atoms Become Unstable
n  p + e (Beta Decay)

21. The End Fate of Medium-Size Stars
Core reaches limits of its ability to sustain fusion
Fusion shells sputter and become unstable
Star expels outermost layers as Planetary Nebulae
Inert core left as white dwarf
Dwarf has such tiny surface area it takes billions of years to cool
Coolest (oldest?) known: 3900 K

22. Tiny Stars
Red Dwarfs are tiny but have huge sunspots and violent flares
They have convection throughout their interiors
Interiors uniform in composition
Do not accumulate helium in core
Can use much more of their hydrogen up
Never fuse He to C
Lifetimes longer than age of Universe

23. Exploding Stars Nova Type I Supernova Type II Supernova
White dwarf attracts matter from neighboring star
Nuclear fusion resumes on surface of star
Many novae repeat at decade or longer intervals
Type I Supernova
White dwarf core resumes fusion
Type II Supernova
Collapse of massive single star

24. Shell Structure of Massive Star
4H –> He
3He –> C
He + C –> O, Ne
Ne + He, C –> O, Mg
2O –> Si
2Si –> Fe

25. Core Collapse Fe core collapses to neutron star in milliseconds
Remaining star material falls in at up to 0.1c
Nuclei beyond Plutonium created
Star blows off outer layers
We see the thermonuclear core of the star
Much of the light is from radioactive nickel

26. Historical Supernovae
185 - Chinese
Chinese, one European record
Chinese, European, Anasazi?
Tycho’s Star
Kepler’s Star
1885 – Andromeda Galaxy
Small Magellanic Cloud (170,000 l.y.)

27. Remains of SN 1054 (Crab Nebula)

28. Life (Briefly!) Near a Supernova
Sun’s Energy Output = 90 billion megatons/second
Let’s relate that to human scales. What would that be at one kilometer distance?
90 x 1015 tons/(150 x 106km)2 = 4 tons
Picture a truckload of explosives a km away giving off a one-second burst of heat and light to rival the Sun

29. Now Assume the Sun Goes Supernova
Brightens by 10 billion times
1010 = 25 magnitudes
Our 4 tons of explosive becomes 40,000 megatons
Equivalent to entire Earth’s nuclear arsenal going off one km away - every second
This energy output would last for days

30. Neutron Stars and Pulsars
Mass of sun but diameter of a few km
Rotate at high speed
Sun 1,400,000 km –> 10 km
Rotation speeds up 140,000 x
28 days –> 17 seconds
Pulsars: infalling matter emits jets of radiation
Millisecond pulsars: probably “spun up” by accretion, or merger of neutron stars

31. How a Pulsar Works

32. Black Holes Singularity: gravity but no size
Event horizon (Schwarzschild radius): no information can escape
Detectable from infalling matter, which emits X-rays
Quantum (atom-sized) black holes may exist
Cores of galaxies have supermassive black holes

33. Black Hole