1. The life cycle of stars from birth to death
Stellar Evolution
The life cycle of stars from birth to death

2. Nebula condense by accretion
Event (shock wave, super nova, etc) triggers nebula collapse

3. ->fusion -> a star
Gas & dust attracts due to gravity Contracting matter causes a spinning & flattening
Large clump in center = forming star
Flat accretion disc = planets
When fusion begins, stellar wind pushes out un-clumped matter and gravitational collapse stops
nebula
Protostar
and disc
Gravity & heat
->fusion -> a star

4. Protostar =forming star; not yet fusing
“glows” from pressure/friction temperatures (not “shining”)

5. Thermonuclear Fusion
Enough heat & gravity = atoms smashed into each other
Universe~80% Hydrogen (H) + 20% Helium (He) + Dust
H + H He + light & heat (Star shines!)
Neutrino—nearly massless particle with no charge
Positron- opposite of an electron; positively charged.

6. Brown Dwarf? = a failed star; never started fusion
Not enough mass in nebula to create enough gravity, pressure and temperature to start fusion
<0.075 Solar mass
Brown Dwarf

7. Main Sequence Star = a fusing “adult” star in equilibrium balance
Gravity pulling in -makes star smaller
Fusion pushing out –makes star bigger
Star size = balance point between gravity & fusion
Fusion
Balloon & N2(l) Demo

8. Day 2

9. Fusion “burning” of atoms
Hydrogen fuel runs out less pressure to hold up gravity
Gravity collapses star heats star fusing bigger atoms
Fusion of Helium into Carbon  greater gas pressure  Star expands to new, bigger equilibrium size

10. Fusing bigger and bigger atoms
As each atom runs out the next large atom can be fused
But requires more gravity to push together
And releases more energy— expands bigger and brighter

11. Main sequence lifespan-all about mass!
Size of nebula determines potential size of main sequence star
Big = blue, hot, bright
use fuel quickly; short lives
Millions of years
Small= red, cool, dim
Use fuel slowly; long lives
Billions-Trillions of years
Our sun =
G class main sequence
Oh Be a Fine Guy/Gal Kiss Me…the reason for the somewhat random letters for star class is because they are the left over letters from a previous classification system. Some letters were dropped and merged and these are the remnants of that first draft system.
Two new classes have been added on the lower end. T and Y? For very cool stars (almost brown dwarfs)
Main Sequence Stars
O B A F G K M

12. Life stages…it’s all about mass!
Our Sun
Small Mass
Big Mass
Biggest Mass

13. Red Giants-the death throws
= Old age star, fusing larger elements
Fusion of larger element more powerful -brighter
Expanded star cools

14. Our sun’s expansion --beyond Earth’s orbit?

15. The End for Small Stars (<8 solar mass) :White Dwarf & Planetary Nebula
Pulsing expansion from Red Giant pushes off outer layers to form a ring cloud =Planetary Nebula
Not enough gravity to fuse bigger atoms-fusion stops
Core contracts to Earth size with no fusion to hold up gravity
Core remains very hot, dim =White Dwarf
Slowly radiates heat until cold = Black Dwarf
The Ring Nebula

16. Black Dwarf= dead core of small mass star; completely cooled (theoretical)
White Dwarf=dead core of a small mass star; still hot but not fusing

17. Day 3

18. Big Mass stars….make Super Red Giants

19. Supernova= collapse & explosion of big mass stars
massive gravity fuses bigger elements up to iron (Fe)
Iron absorbs heat & cools star
Rapid cooling collapses the core
Collapsed core creates a shockwave –colliding atoms creates all elements bigger than iron (Fe)

20. All elements beyond H from stars
#1 Made in Big Bang
#2-26 Made by fusion in stars
All others Made in Supernova

21. Big Stars end as…Neutron Stars (9-20 solar masses)
No more fusion to hold up gravity
Gravity strong enough to collapse dead core until atoms crushed to neutrons
Extremely dense- size of a city

22. Most massive stars die as a Black hole
No fusion to hold up gravity
Gravity so strong that all mass crushed into itself down to a point
Gravity so strong not even light can escape

23. HR Diagram-plots star temp vs brightness

24. HR Diagram -plots star temp vs brightness

25. Planet & Sun Size Comparison