Announcements
•Exam 3 is scheduled for Wednesday April
8. Will be pushed back to Monday April 13
Tentatively will cover the rest of Chapter 4
and all of Chapters 5 & 6. Sample
Questions will be posted tomorrow.
•1st Quarter Observing Night Thursday
night. Set-up starts at 6:30 if clear, 6:45 if
cloudy.
Colored Card Questions
ClassAction website
ISM & Star Formation module
Star Formation Masses
Emission Nebula Energy Source
Stellar Properties II module
Stellar Parameters
HR Groups
Life beyond the Main Sequence
What happens when a star runs out
of hydrogen fuel in its core?
With no more hydrogen fusion
occurring in the core, hydrogen fusion
continues in a shell around the core
Energy imbalance from
shell hydrogen fusion
creates a Red Giant
Helium Fusion starts when
core reaches 100,000,000°
The higher
temperature is
needed to
overcome the
stronger electric
repulsion
between the
nuclei
Triple Alpha Helium Fusion
4
He  He  Be
4
8
8
Be  He C  
4
12
3 He C  
4
12
Additional Fusion involving He
C  He O  
12
4
16
Ash from Helium Fusion:
Carbon & Oxygen
Helium fusion begins
differently for some stars
The determining factor is whether or not the
core becomes degenerate
Normal versus
degenerate
electron energy
levels
Degeneracy
•Electron energy levels crowded together
almost continuous
•All low energy levels are full
Pauli Exclusion Principle
•Only place for additional electrons to go is
in high energy levels which means
they must be moving at close to the
speed of light
•Adding more mass decreases the volume
•Temperature is same everywhere
Evolution on an H – R Diagram
Helium
Flash
For low mass stars: a second
red giant stage
The second red giant phase begins when the
helium fuel in the core is exhausted and core fusion
once again stops
Internal Structure of AGB
star
Convection in
final stages
dredges up
products of
earlier fusion
and ejects it
into space
Thermal Pulses cause whole
layers of a star to lift off
Stars recycle most matter
back out into the universe
Planetary Nebulae form from
low mass stars (<8Msun)
In the end, only the cooling core is
left: a white dwarf star
X-ray
Canis Major
Visible
Colored Card Questions
ClassAction website Stellar Evolution module
HR Evolutionary Track
HR Movement
Core Stages 1
Core Stages 2
White dwarf stars are
planetary size but stellar mass
White Dwarf Stars are
degenerate matter
Chandrasekhar Limit
1.4 Msun
The evolutionary path of white
dwarf stars are cooling curves
A white dwarf in a binary
system can be revived to
become a cataclysmic variable
For stars with mass >8Msun
Carbon fusion begins at
600,000,000°
Carbon fusion produces Oxygen,
Neon and Magnesium
Higher fusion requires higher
temperatures and takes less time
Internal Structure becomes
layered like an onion
Once iron starts to form energy is
no longer produced
When
the iron
core
reaches
1.4 solar
masses
the end
comes
swiftly
The End: Photo-disintegration
and Reverse Beta Decay
Fe  High Energy   He
4
e  p  n 


Type IIa Supernova
Watch Supernova videos