Download Final Stages of Stellar Evolution - supernovae and the synthesis of

Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Final Stages of Stellar Evolution
supernovae and the synthesis of heavy nuclei
Benjamin Klein
University of Karlsruhe
06.XII.2006
Seminar on Astroparticle Physics - Cosmic Rays
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Introduction
What happens to stars which run out of
fuel?
What are supernova explosions and which
different types exist?
Where do heavy elements come from?
For Take Away
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Outline
1
Nucleosynthesis
Revision of Nucleosynthesis up to Iron
Nuclear Synthesis of Heavy Elements
2
Supernova Explosions
White Dwarfs
Classification of Supernovae
3
Final Stages of Stellar Evolution
Neutron Stars
Black Holes
For Take Away
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Outline
1
Nucleosynthesis
Revision of Nucleosynthesis up to Iron
Nuclear Synthesis of Heavy Elements
2
Supernova Explosions
White Dwarfs
Classification of Supernovae
3
Final Stages of Stellar Evolution
Neutron Stars
Black Holes
For Take Away
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Outline
1
Nucleosynthesis
Revision of Nucleosynthesis up to Iron
Nuclear Synthesis of Heavy Elements
2
Supernova Explosions
White Dwarfs
Classification of Supernovae
3
Final Stages of Stellar Evolution
Neutron Stars
Black Holes
For Take Away
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Outline
1
Nucleosynthesis
Revision of Nucleosynthesis up to Iron
Nuclear Synthesis of Heavy Elements
2
Supernova Explosions
White Dwarfs
Classification of Supernovae
3
Final Stages of Stellar Evolution
Neutron Stars
Black Holes
For Take Away
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Primordial Nucleosynthesis
within the first 3 minutes after the Big Bang
synthesis of light elements
neutron/proton ratio of 1:7
most neutrons → He
most remaining protons → H
only traces of heavier elements
nuclear magic numbers A = 5 and A = 8
photodissociation of heavier elements
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Nucleosynthesis
Supernova Explosions
Stellar Nucleosynthesis
synthesis of elements up to iron
proton-proton chain
CNO cycle
nuclear burning in different zones
onion structure
Final Stages of Stellar Evolution
For Take Away
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Outline
1
Nucleosynthesis
Revision of Nucleosynthesis up to Iron
Nuclear Synthesis of Heavy Elements
2
Supernova Explosions
White Dwarfs
Classification of Supernovae
3
Final Stages of Stellar Evolution
Neutron Stars
Black Holes
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
s-process (1)
process of neutron capture
neutrons preferentially captured by heavy nuclei
base material eg. iron
nucleus becomes instable → β − -decay
slow-process
“low” neutron flux (105 − 1011 neutrons
)
s·cm2
“low” temperatures (∼ 3, 000, 000K)
β − decay before next neutron is captured
conditions met in red giant stars
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
s-process (2)
moving along the valley of stability
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Nucleosynthesis
Supernova Explosions
s-process (3)
Final Stages of Stellar Evolution
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
s-process (4)
limitations of the s-process
not all heavy elements can be
synthesized in the s-process
heavy nuclei, eg. thorium or
uranium, decay several times before
repeated neutron capture
ends in bismuth cycle
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
s-process (5)
Nuclear Astrophysics at FZK
research group of Dr. Käpperle at FZK
measurements of cross sections for
neutron capture
ratification of models for red giant stars
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
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r-process (1)
rapid-process
high neutron flux (∼ 1022 neutrons
)
cm2 ·s
high temperatures
multiple neutrons captured before β − -decay
possible places where r-process could take place
supernovae II (T ∼ 109 K )
collision of two neutron stars
abundance of r-process elements indicates that...
only small quantity of supernovae returns elements to the
outside
every supernovae exposes only a small fraction of its
synthesis products to the outside
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
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r-process (2)
processes slowing down the r-process
heavy isotopes unstable because of spontaneous fission
(A ' 270)
→ r-process ends
neutron drip line → separation energy En = 0
closed neutron shells at N = 50, 82, 126
probability of capture sinks
confirmation: higher abundance for this neutron numbers
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
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r-process (3)
magic neutron numbers:
N = 82, N = 126
s-process:
A = 138 (Barium)
A = 208 (Lead)
r-process:
A = 130 (Cadmium)
A = 195 (Thulium)
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
(r)p-process
have to overcome coulomb barrier
p-process
photodisintegration process
(γ, n), (γ, α)
supernovae
temperatures T ∼ 3 · 109 K
p-only isotopes, eg. 190 Pt(Platinum), 168 Yb(Ytterbium)
rp-process
proton captures onto seed nuclei
hydrogen rich environment
surface of a white dwarf or neutron star
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Nucleosynthesis
Supernova Explosions
Neutron Capture Processes
Final Stages of Stellar Evolution
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Outline
1
Nucleosynthesis
Revision of Nucleosynthesis up to Iron
Nuclear Synthesis of Heavy Elements
2
Supernova Explosions
White Dwarfs
Classification of Supernovae
3
Final Stages of Stellar Evolution
Neutron Stars
Black Holes
For Take Away
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
White Dwarfs (1)
intermediate state of a dying low or medium
mass star
inner core of former red giant star
consists mostly of carbon and oxygen
not heavy enough to fuse carbon
after fusion stops only electron degeneration
pressure supports core against gravitational
collaps
pdegeneration ∼ pgravitation if
Mstar ≤ 1.4 · M ≡ MChandrasekhar
if Mstar > MChandrasekhar → supernova
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
White Dwarfs (2)
approximately the size of the Earth
0.5 − 0.6M
ρ ∼ 109 mkg3
Rwhite dwarf ∝
1
M 1/3
extremely hot (∼ 20, 000K) with small
surface
→∼ 25 billion years to cool down
final state: black dwarf
For Take Away
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Outline
1
Nucleosynthesis
Revision of Nucleosynthesis up to Iron
Nuclear Synthesis of Heavy Elements
2
Supernova Explosions
White Dwarfs
Classification of Supernovae
3
Final Stages of Stellar Evolution
Neutron Stars
Black Holes
For Take Away
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Supernovae
stellar explosion which involves the whole
star
two mechanisms
stars with Mstar > 8 · M
→ after extinction of nuclear fuel
→ core collapse
white dwarfs with Mstar < 8 · M in binary
system with red giant
→ accretion of matter
→ multiple nova explosions
→ supernova
20 ± 8 supernovae per millenium in the
Milky Way (2/3 visible)
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Classification
classification in 1939 by Rudolph
Minkowski
two types with subtypes by chemical
experiments in their spectra
SN Type I: without hydrogen
Balmer line
Ia: no hydrogen, strong silicon
Ib: weak hydrogen, strong helium
Ic: no hydrogen, no helium, weak
silicon
SN Type II: with hydrogen Balmer
line
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
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Naming of Supernovae
prefix “SN” followed by year of discovery
first 26 supernovae upper case letter from A to Z
following combination of lower case letters aa to zz
eg. SN1987A was the first observed supernova in 1987
last supernova in 2005: SN2005nc
november 2006: SN2006ot
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Novae
close binary system of a white dwarf and a red
giant
cataclysmic nuclear explosion caused by
accretion of hydrogen
hydrogen compacts on the surface of the white
dwarf under high pressure and temperature
fusion (CNO-cycle)
heavier fusion products remain on the surface
remaining gas is blown away from the surface
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Supernovae Ia (1)
same preconditions as for nova
heavy elements as fusion products of
novae remain on the surface
→ increasing mass
mass slightly under MChandrasekhar
→ nuclear fusion reaction of carbon and
oxygen
white dwarf supported against gravity by
quantum degeneray pressure
no expansion → no cooling
unregulated fusion
thermonuclear supernova
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Supernovae Ia (2)
no remaining compact massive object
companion star escapes with orbital velocity ∼ 100 km
s
→ “runaway star”
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Supernovae Ia (3)
Supernova Cosmology Project
SN Ia always same absolute magnitude
→ standard candles
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Supernovae II
hydrogen Balmer line visible
stars ∼ 8 − 30 · M
stars heavy enough for fusion up to
iron
reach always Chandrasekhar limit
(∼ 0.9M )
core collapse
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Core Collapse (1)
Collapse Accelerated by Two Processes
photodisintegration
photodissociation of iron nuclei by
high energy γ-rays
γ +56 Fe → 134 He + 4n
γ +4 He → 2p+ + 2n
high binding energy of iron
→ requires energy
radiation pressure decreases
inverse β-decay
e− + p → n + νe
loss of free electrons
decreasing pressure
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Core Collapse (2)
core collapse takes only some milliseconds
in a distance of 20-50 km of the center pressure
not high enough for matter to respond
vmatter > vsound
shock wave
because of photodissociation mostly neutrons in
the inner core
→ degeneration pressure
→ core almost instantanously incompressible
shockwave reflected
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Nucleosynthesis
Supernova Explosions
Core Collapse (3)
Final Stages of Stellar Evolution
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Core Collapse (4)
high temperature gas & neutrons from the center
→ r-process
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Core Collapse (5)
Cooling of the Inner Core
electron/positron pair production
2γ → e+ + e−
high cross section → cannot escape
re-annihilation
neutrino/antineutrino pair production
2γ → ν + ν̄
can finally escape → cooling
liberated gravitational binding energy
99% in neutrinos
1% kinetic energy of explosion
0.01% photons
neutrino luminosity L ∼ 3 · 1053 erg/3sec ∼ 3 · 1019 L
For Take Away
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Core Collapse (5)
Observation of Supernovae
observation of neutrinos before optical
detection
scattering of ν and γ
cross section σγ σν
SN1987A: Kamiokande II
SuperNova Early Warning System
(SNEWS)
Super-Kamiokande
LVD
SNO
AMANDA
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Subtypes of Supernovae II
supernovae II-P
high ejected mass and velocity of shell
decreasing luminosity compensated by
fast expanding shell
light curve shows plateau domain
maximum luminosity strongly connected
to radius of progenitor star
→ peak value of luminosity widely spread
supernovae II-L
low expansion velocity
linear decreasing luminosity
marginally spread peak luminosity
For Take Away
Nucleosynthesis
Supernova Explosions
Supernovae Ib/Ic
stars with mass > 30 · M
Wolf Rayet phase
core collapse as in SN II
supernova Ib/Ic
Final Stages of Stellar Evolution
For Take Away
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Outline
1
Nucleosynthesis
Revision of Nucleosynthesis up to Iron
Nuclear Synthesis of Heavy Elements
2
Supernova Explosions
White Dwarfs
Classification of Supernovae
3
Final Stages of Stellar Evolution
Neutron Stars
Black Holes
For Take Away
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Neutron Stars (1)
neutron stars proposed by Walter Baade
and Fritz Zwickly in 1933
mass of 1.35 − 2.1M
radius ∼ 10 − 20km (R ∼ 106 km)
high rotation speed (∼ 1/700 − 30sec)
because angular momentum conserved
escape velocity ∼ 150, 000km/s
supported by neutron degeneration
pressure
slowing down between
10−10 − 10−21 sec/rotation
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Neutron Stars (2)
Different Types Of Neutron Stars
x-ray bursters
neutron star in binary system accreting matter from
companion star, causing irregular X-ray bursts
pulsars
neutron star emitting pulses of radiation
magnetars
neutron star with extremly strong magnetic fields
magnetic fields of ∼ 100GT
rotation period ∼ 5 − 12sec
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Pulsars (1)
first pulsar discovered by Jocelyn Bell
Burnell and Antony Hewish in 1967,
PSR1919+21 “LGM-1”
very regular periodical signal detectable
radio array → pulses of radiation
solution: rotating neutron stars
sources of energy
rotation powered pulsars
accretion powered pulsars → X-rays
magnetic powered pulsars
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Nucleosynthesis
Pulsars (2)
Supernova Explosions
Final Stages of Stellar Evolution
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Pulsars (3)
Millisecond Pulsars
in 1982 discovery of millisecond pulsars “MSPs”
rotation periode ∼ 1.6ms
extraordinarily stable rotation
→ astronomical clocks
measurement of gravitational waves
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Crab Nebula (1)
observed by John Bevis in 1731, Earl of
Rosse in the 1840s
SN1054
pulsar in its centre (∼ 30rounds/sec)
radiation from gamma rays to radio waves
progenitor star 8 − 12M
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Crab Nebula (2)
filaments remnants of the progenitor star’s
atmosphere
ionised helium and hydrogen, carbon, oxygen,
nitrogen, iron, neon, sulphur
density ∼ 1, 300particles/cm3
diffuse blue region → synchroton radiation
pulsar → strong magnetic field
radiation used for studying objects that occult it
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Nucleosynthesis
Supernova Explosions
Crab Nebula (3)
Studying Objects that Occult the Crab Nebula
Final Stages of Stellar Evolution
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Nucleosynthesis
Supernova Explosions
Crab Nebula (4)
Path of Titan in 2003
Final Stages of Stellar Evolution
For Take Away
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Outline
1
Nucleosynthesis
Revision of Nucleosynthesis up to Iron
Nuclear Synthesis of Heavy Elements
2
Supernova Explosions
White Dwarfs
Classification of Supernovae
3
Final Stages of Stellar Evolution
Neutron Stars
Black Holes
For Take Away
Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Black Holes (1)
body so massive that light can’t escape
concept by English geologist John Michell
in 1784
collapse of neutron star > 3 · M
→ Tolman-Oppenheimer-Volkoff limit
Schwarzschild Radius RSchwarzschild =
event horizon
theory of general relativity
curvature → ∞
singularity at the center
2GM
c2
For Take Away
Nucleosynthesis
Supernova Explosions
Black Holes (2)
Light Cone
Final Stages of Stellar Evolution
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Nucleosynthesis
Supernova Explosions
Black Holes (3)
Final Stages of Stellar Evolution
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
Black Holes (4)
Supermassive Black Holes
supermassive black holes
in center of most galaxies
→ collapse of dense cluster of stars
large amouts of mass accreting onto
stellar “seed” black hole
fusion of smaller black holes
masses up to 109 · M
jets
acceleration of high energetic cosmic
rays
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Nucleosynthesis
Supernova Explosions
Final Stages of Stellar Evolution
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Diffrent types of supernovae: core collapse vs.
thermonuclear supernovae
Supernovae Ia used as cosmic standard candles.
Final stages of stellar evolution are black dwarfs, neutron
stars and black holes, depending on the mass of the star.
Heavy elements produced in the s-process in red giant
stars and in the r-process in supernova explosions.