Transcript SES4U Life Cycle of a Star

 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
1.
2.
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4.
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
1.
2.
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)
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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
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
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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.
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Entirely dependent on the initial mass of the star
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Low mass stars do not have conditions to fuse He
into C
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Outer layers puff away creating planetary nebula
The Sun dies
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Entirely dependent
on the initial mass
of the star
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Massive stars are
able to create iron
cores over the span
of their lifetime
and may
supernova
(explode)
Crab Supernova & Cassiopeia Explosion
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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)
(http://www.valdosta.edu/~cbarnbau/astro_demos/stellar_evol/evol_2.html)
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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
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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
(http://www.valdosta.edu/~cbarnbau/astro_demos/stellar_evol/evol_3.html)
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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
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
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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
• Wien’s Law Graph
• Wien’s Law Practice
•P. 851 Q: 3 and 5