1. 2. What does the word “Evolution” mean?
Bellwork 11/16: If you borrowed a book, please check it in and put it back in the cabinet 
1. Describe the basic steps of Stellar Formation (notes from last time).
2. What does the word “Evolution” mean?

2. Quick and Friendly Reminder…
Consider a Unit 2 Test retake
Take a reassessment ticket & sign up for ASR
Communicate with me, please 

3. What’s Coming Up? Today: Review Stellar Formation
Stellar Evolution Part 2: Life Cycles of Stars!
Lab
Monday:
Lab Comprehension Quiz—did you understand the lab?
Stellar Evolution Part 3: Death & Nucleosynthesis
Wednesday:
Gravity!
Everything we’ve talk about so far…PULLED TOGETHER 

4. Let’s recap stellar formation

5. Discuss with your table partner:
Based on your reading from the book, match each phase of a human life cycle with each phase of a star’s life cycle.
Human Life Cycle Stages
Stellar Life Cycle Stages
Gamete
Fetus
Childhood-Young Adult Hood
Middle Age
Old Age-Death
Red Giant/Supergiant
Fusion Ignition/Main-sequence
Nebula
Stellar Remnant
Protostar

6. Stellar evolution Changes in a star’s properties over its “life”
Stars exist because of gravity
Two opposing forces in a star are
Gravity – contracts
Thermal nuclear energy – expands

7. Stages (5 Total) Nebula Birth In dark, cool, interstellar clouds
Gravity contracts the cloud
Temperature rises

8. Stages
2. Protostar
Gravitational contraction of gaseous cloud continues
Hydrogen nuclei fuse
Become helium nuclei
Process is called hydrogen burning
Energy is released
Outward pressure increases

9. WAIT! Do all protostars become stars?
Nope!
Sometimes a protostar does not have enough mass to start hydrogen fusion
These “stars” are known as Brown dwarfs
Comparable to Jupiter in size& one millionth the luminosity of the sun

10. 3. Main-sequence stage
When outward thermal energy pressure is balanced by gravity pulling inward
Hydrogen continues to fuse into Helium
Luminosity & Temperature are dependent on this “fuel”
90% of a star's life is in the main-sequence
Questions 1 & 3
There are lots of types of Main-sequence stars. Why? What determines where they fall on the H-R Diagram?

11. Main Sequence Stars—a closer look
Question 2
Main Sequence Stars—a closer look
We said that all stars are made up of mostly H & He…and yet…
There are lots of types of Main-sequence stars…why?
More mass = more fuel = more energy is radiated

12. 4. Red giant stage Questions 4-7 Hydrogen burning migrates outward
Star's outer envelope expands
Surface cools & becomes red
Core is collapsing as helium is converted to carbon
Eventually all nuclear fuel is used
Gravity squeezes the star
Unbalanced forces
Questions 4-7

13. 5. Burnout or Death OPTIONS:
White Dwarf
Planetary Nebula
Supernova
Black Hole
Neutron star
What determines which of these outcomes will occur?
Let’s take a look…

14. Stellar Evolution Simulation
You will begin as 1 of 4 main-sequence type stars
You will travel through stations, recording your star’s evolution
You will be collecting information on intermediate and ending phases

15. The Basics: You will want to have your labeled HR-Diagram handy 
Choose a “star” out the beaker. Determine which type of star you are based on the data given & your HR Diagram
Mass Luminosity Temp.
2. Follow the directions at each table.
3. Make sure to collect information at each station
4. Record your evolutionary pathways on the class data table, please.

16. You can start out as 1 of 4 stars:
Brown Dwarf
Red Dwarf
Average/Solar-type
Blue Supergiant
Note: these stars are on the main-sequence…

17. Class Data—2A: Began As… Evolutionary Pathway… Brown Dwarf Red Dwarf
Average (Solar-Type)
Blue Supergiant

18. Class Data—1A: Began As… Evolutionary Pathway… Brown Dwarf Red Dwarf
Average (Solar-Type)
Blue Supergiant

19. What do we notice about the class data?

20. Stellar Remnants

21. White Dwarf Small (some no larger than Earth) Dense
Can be more massive than the Sun
Spoonful weighs several tons
Atoms take up less space
Electrons displaced inwards

22. Neutron Star Forms from a more massive star Remnant of a supernova
Star has more gravity
Squeezes itself smaller
Remnant of a supernova
Gravitational force collapses atoms
Electrons combine with protons to produce neutrons
VERY Small size

23. Neutron Star
Pea size sample
Weighs 100 million tons

24. Black Hole More dense than a neutron star
Intense surface gravity lets no light escape
As matter is pulled into it
Becomes very hot
Emits x-rays
Likely candidate is Cygnus X-1, a strong x-ray source