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Chapter 12
Stellar Evolution/
Supernovae
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Outline
• Test 3 Wednesday
• Death of Low-mass Stars
• Death of High-mass Stars
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Current Events
• http://apod.nasa.gov/apod/ap111109.html
• http://www.youtube.com/watch?feature=pla
yer_embedded&v=vtEvuz_oQ5o
• http://www.space.com/scienceastronomy/g
reen-brown-dwarf-star-spotted101110.html
• http://news.discovery.com/space/top-5space-spirals.html
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Figure 12.10
White Dwarf
on H–R Diagram
12 - For 1 solar mass
stars, that is all that
will fuse.
•
(need 600 million K
for the next reactions
to occur.)
•
The outer shell gets
“blown off” by the
hot, dense, core.
•
Result is a planetary
nebula around a
white dwarf (13).
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Figure 12.9
Planetary Nebulae
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Figure 12.12
Distant White Dwarfs - globular cluster M4
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Figure 12.11
Sirius Binary System - nearby example of a white dwarf
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Figure 12.14
Close Binary System
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Figure 12.13ab
Nova
•
•
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A nova forms when
the temperature in
the accretion disk
reaches 107 K (H
fusion).
Such a star might
“go nova” dozens (if
not hundreds) of
times.
Figure 12.13c
Nova
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Figure 12.15
Nova Matter Ejection
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High Mass Stars
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Figure 12.16
High-Mass
Evolutionary Tracks
•
•
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Intermediate mass
(~4 Msun) stars fuse
carbon, but end up
as white dwarfs.
High mass (>10 Msun)
stars evolve rapidly.
Helium (and other)
fusion begins before
the star ever gets to
the Red Supergiant
stage.
Figure 12.16
High-Mass
Evolutionary Tracks
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•
Wolf Rayet stars (are
really big ones) have
very strong winds.
•
http://upload.wikimedia.org/wi
kipedia/commons/4/49/Crescen
thunter.jpg
When fusion is happening in the core of a
star, the core is
A) heating and shrinking
B) heating and expanding
C) cooling and expanding
D) in equilibrium
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When fusion is happening in the core of a
star, the core is
A) heating and shrinking
B) heating and expanding
C) cooling and expanding
D) in equilibrium
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When fusion stops in the core of a star,
the core is
A) heating and shrinking
B) heating and expanding
C) cooling and expanding
D) in equilibrium
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When fusion stops in the core of a star,
the core is
A) heating and shrinking
B) heating and expanding
C) cooling and expanding
D) in equilibrium
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Figure 12.17
Heavy Element Fusion
•
Each stage is faster
than the stage
before.
•
•
•
•
•
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H - 10 million years
He - 1 million years
C - 1000 years
O - 1 year
Si - 1 week
Figure 12.17
Heavy Element Fusion
•
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Fusion of iron does
not produce energy!
Core-Collapse
• The iron core shrinks and heats.
• Photons are energetic enough to photodissociate iron nuclei.
• Iron converted back to protons and
neutrons.
• This uses up energy - reduces pressure
• Collapse accelerates!
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Core-Collapse
• Protons and electrons combine to form
neutrons releasing neutrinos.
• Collapse continues until neutrons are in
contact with each other.
• Core “rebounds” and a shock wave throws
off the outer layers of the star (mostly H
and He.)
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Core-Collapse
• Protons and electrons combine to form
neutrons releasing neutrinos.
• Collapse continues until neutrons are in
contact with each other.
• Core “rebounds” and a shock wave throws
off the outer layers of the star (mostly H
and He.)
• This collapse takes about 1 second!
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Figure 12.18
Supernova 1987A
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Recent Supernovae
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Recent Supernovae
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Figure 12.19
Supernova Light Curves
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Figure 12.20
Two Types of Supernova
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Carbon Detonation (Type I) Supernova
• Recall the accretion around a white dwarf
star.
• When the star reaches 1.4 Msun, the
density and temperature allow carbon to
finally fuse.
• It fuses everywhere simultaneously.
• Almost no hydrogen observed in the
spectrum of Type I supernova.
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Figure 12.21
Supernova Remnants
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Formation of Heavy Elements
• Elements heavier than iron require energy
input for creation.
• Supernovae provide the energy source.
• The expanding cloud contains primarily H
and He, but is enriched in heavy elements.
• The Sun was created from “enriched”
interstellar gas and dust.
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More Precisely 12-1
The Cycle of Stellar Evolution
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Three Minute Paper
• Write 1-3 sentences.
• What was the most important thing
you learned today?
• What questions do you still have
about today’s topics?
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