Transcript Friday, Oct 31

Lecture 22 –
Stellar Evolution
HST: Pne - Red Rectangle
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Star Fleet Academy
Tues: Nov 4, 18, 25
Noon
Alllen 326
Couldn’t get into
PHYS 1830?
Enrollment limit has
increased.
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Come take up your –
test. Monday 3pm
Allen 514 or by
appointment
(email about time).
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Read before class:
Star Birth Chapt 18 and 19
Stellar Evolution M ~1 Msun (PN & WD): Chapt 20
massive star death (SNe): Chapt 21
stellar populations Chapt 23 (p. 587)
Gamma-ray bursts & black holes Chapt 22 –
REVIEW GR model of gravity
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STAR
Stellar Evolution: Star Death
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• Recall Stefan-Boltzmann Law
• r == stellar radius
• T == surface temperature
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Leaving the MS
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• H converted to He in core
 no pressure P to counter gravity
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 Red Giant
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• Helium fuses  Carbon
• Equilibrium
• Horizontal Branch on HR diagram
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What will happen?
Part way through the evolution of 1 solar mass – last lecture to here.
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Planetary Nebula (PN, plural Pne):
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• UV photons from core ionize expanding
shell
• Gas disperses ~3*10**4 yr
• Remnant of PN  White Dwarf
White Dwarf (WD):
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Remnant of PN
size of Earth, mass of ½ sun
initially hot but not luminous
r contraction stops, supported by electron degenerate
P
• T decrease, L decrease
 expect Black Dwarf
Electron degenerate P only support up
to 1.4 Msun == Chandrasekar Limit.
Stars M < 5 Msun become WD
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Stellar Evolution and the H-R Diagram: 1 solar mass
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• Evolution of a 1 solar mass star.
• Main Stages:
– Red Giant
– Planetary Nebula
– White Dwarf
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Red Giant Stage:
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• Radius increases.
– to orbit of Jupiter
• Surface T decreases.
• fusion of He in core  Carbon (C)
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Planetary Nebula
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Model
• Ejected outer envelope.
• Core of star is revealed.
• Hot core ionizes expanding
envelope.
The Eskimo Nebula:
•Lasts ~ 30 * 10**4 yrs.
•Radius 0.25 to 2 ly.
View from side: Bipolar
Hubble 12
HST/WFC3
View from side: Bipolar
On right: HST/WFC3 + ALMA
ALMA (yellow) shows carbon torus.
Red Rectangle Planetary Nebula (ESA/Hubble Image of the Week)
How do they get bipolar shape?
ATCA
Old sun-like star with jets!
Jet of particles spiralling in strong B field  shape of nebula.
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White Dwarf Stage:
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HST
Binary system of
Sirius A and Sirius B
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Sirius B.
High T, low L  R very small (e.g. size of Earth).
The stellar core after the PN has dissipated.
Contracts  Degenerate Electron Gas: electrons
packed as tightly as possible.
• Pressure support since negative charges repulse each
other.
• Fades over 100s * 10**9 yrs.
Stellar Evolution of a 1 solar mass star:
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• The position of a star on the HR
diagram changes as the star evolves.
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Evolution of Stars with Mass > 5 Solar Masses
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Supernovae
– violent explosions
– outshine host galaxy
–  distances for cosmology
–  responsible for heavy elements in
universe
– 2 main types
Supernova Type Ia
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• 2 scenarios involving binary systems
1. a giant & white dwarf
2. two white dwarfs merging
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Supernovae
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Type
Ia
Scenario 1.
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• most stars in binary star systems
 giant & white dwarf.
• Roche Lobe: Tear-drop shaped zone of influence of a
star i.e. material within lobe “belongs” to that star.
• Lagrangian point: gravitational pull of the 2 stars
balances the rotation of the binary system. Material
can flow through this point.
Supernovae
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Type
Ia
Scenario 1.
• Tenuous material from giant falls onto WD
• Limit to mass support
Chandrasekhar limit ~ 1.4 Msun
• as soon as mass on WD increases beyond this
 core contract
 T increase on surface to required for fusion
 detonation all at once, blowing WD apart
 no remnant
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Supernovae Type Ia: Scenario 1
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• Exceeding Chandrasekhar limit 
runaway fusion totally destroying WD
Supernovae Type Ia: Scenario 2
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• Double Degenerate: 2 white dwarfs
merging
• Exceeding Chandrasekhar limit 
runaway fusion totally destroying WD
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• Chandra X-ray observations
Supernovae Type Ia
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• ~1.4 Msun  small range of intrinsic
luminosity for peak
• shape of the light curve distinguishes
SNe types
Supernovae Type Ia
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• Inverse Square Brightness Law  distance to
host galaxy.
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Big Bang: The Expansion of the Universe:
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Observations
The expansion is accelerating!
SNe distance vs Doppler-shifted velocity (redshift = v/c)
 Hubble Law & expansion
 Dark Energy
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2011 Nobel prize winner!
• Brian Schmidt, Saul Perlmutter, and
Adam Reiss for finding that the
universe’s expansion is accelerating.