1. Life Cycle of a Star

2. Life Cycle of a Star: Protostar
A nebula (97% H, 3% helium) contains regions where matter clumps.
Clumping of matter into a protostar (young, precursor) is called ACCRETION
The protostar must achieve equilibrium between gas pressure and gravity

3. Life Cycle of a Star: Protostar

4. Life Cycle of a Star: Protostar
Gravity pulls gas and dust inward toward the core.
Inside the core, temperature increases as gas atom collisions increase and density of the core increases.
Gas pressure increases as atomic collisions and density (atoms/space) increase and the protostar’s gas pressure RESISTS the collapse of the nebula.
When gas pressure = gravity, the protostar has reached equilibrium and accretion stops

5. Life Cycle of a Star: Protostar
If critical temperature in the core is not reached, the protostar becomes a brown dwarf and never reaches star status
If critical temperature is reached, nuclear fusion begins (H fuses into He for the first time)

6. Life Cycle of a Star: Main Sequence
Stars will spend the majority of their lives fusing H into He
When H fuel is gone, He is fused into C
Massive stars are able to fuse C into heavier elements
Stars slowly contract as they release energy during their life, yet their internal temperatures, densities and pressures continue to increase in the core
HiLo Star Animation

7. Life Cycle of a Star: Main Sequence
Larger stars have more fuel, but they must burn this fuel faster to maintain equilibrium
Fusion happens at an accelerated rate in massive stars and therefore they use up their fuel supply in a shorter amount of time
Bottom Line:
Large stars burn bright and die young
Small stars burn consistently and live long

8. Life Cycle of a Star: Main Sequence
Throughout its life, a star oscillates between stable and unstable states
Nuclear Fusion. Gas pressure=Gravity
Fuel (H and He for small-medium stars; C-Fe in massive stars) runs out
Fusion stops and temperature decreases
Core contracts
Increase in temperature and density due to increased particle collisions reignites the process.

9. Life Cycle of a Star: Old Age and Death
Entirely dependent on the initial mass of the star
Low mass stars do not have conditions to fuse He into C
Outer layers puff away creating planetary nebula
The Sun dies

10. Life Cycle of a Star: Old Age and Death
Entirely dependent on the initial mass of the star
Massive stars are able to create iron cores over the span of their lifetime and may supernova (explode)
Crab Supernova & Cassiopeia Explosion

11. Low-Mass Stars 0.5 solar mass or less
Outer layers puff away and become planetary nebulae.
Eventually become white dwarves (about the size of Earth)
Steadily decrease in diameter throughout life (no creation of planetary nebulae, no expansion, no supernova) (

12. Medium-Mass Stars 0.5 solar mass to 3.0 solar mass
Gradually expands into a red giant / supergiant
Outer layers puff away and may leave a white dwarf
May supernova and become neutron stars (neutrons prevent future fusion reactions and create immensely dense conditions)
Neutron stars are much smaller than Earth

13. Massive Stars 3.0 solar masses or larger
Expands into a red supergiant,
Contracts and supernovas
Nebular material is contracted back to the center of the star creating a black hole.
Supernova / Hypernova?!?!!!!
May become a large neutron star, then upon a secondary supernova become a black hole (

14. From Yesterday Graphing Sunspots Hertzsprung Russell Diagram
Data Analysis Lab on page 835
GeoLab on page 853
Identify the unknown elements
Complete Analyze and Conclude Q:1-3

15. Wien’s Displacement Law
Wavelength distribution of energy from a black body (emits all wavelengths) at any temperature is of a similar shape, but of a different distribution (1 x 109 nm = 1 m)
T is the absolute temperature (K) of the black body
b is a constant called Wien's displacement constant, equal to 2.90 ×10−3 m·K
λmax = b / T
Wien's displacement law implies that the hotter an object is, the shorter the wavelength of its most emitted type of radiation

16. Wien’s Law Graph Wien’s Law Practice P. 851 Q: 3 and 5
Homework:
Wien’s Law Graph
Wien’s Law Practice
P. 851 Q: 3 and 5