2. Supernova（超新星）
•Supernova explosion is very luminous!
•The energy which a supernova emits is
roughly J
1043
•Remember that the sun emits energy
4 × 1026
J/s
How many solar years of energy are released
in a supernova explosion?
(Calculation)
(Answer)
2
3. Supernova（超新星）
•Supernova explosion is very luminous!
•The energy which a supernova emits is
roughly J
1043
•Remember that the sun emits energy
4 × 1026
J/s
How many solar years of energy are released
in a supernova explosion?
(Calculation)
(Answer)
t ∼
1043
4 × 1026
∼ 108
− 109
years
2
5. Type I supernovae
Type II supernovae
•There are two kinds of supernova.
Low hydrogen
Lots of hydrogen
Supernova（超新星）
3
6. Type I supernovae
Type II supernovae
•There are two kinds of supernova.
Low hydrogen
Lots of hydrogen
•Type II supernovae usually have a characteristic “plateau” in the light curve a few months
after the maximum.
Plateau
Supernova（超新星）
3
7. Type I supernovae
Type II supernovae
•There are two kinds of supernova.
Low hydrogen
Lots of hydrogen
•Type II supernovae usually have a characteristic “plateau” in the light curve a few months
after the maximum.
Plateau
What is the difference in mechanism between Type I supernovae and Tye II supernovae?
Supernova（超新星）
3
8. Type I supernovae
Type II supernovae
The mechanism of Type I supernovae and Type II supernovae is different!
But, the total amounts of energy of Type I supernovae and Type II supernovae are similar.
All high-mass stars ( )
≳ 8M⊙
Only a few fractions of low-mass stars
Although only a few fractions of low-mass stars become Type I supernovae, the rate of
the two types of supernovas is roughly the same because the number of low-mass stars is
much higher than high-mass stars.
Same rate!
Supernova（超新星）
4
10. Supernova Remnants（超新星遗迹）
SN1054
Cassiopeia A
•We can observe supernova remnants as evidence of supernovae in our galaxy.
•Although we can only observe the supernova remnant of SN1054 now, Chinese astronomers
reported that SN1054 occurred in 1054. 5
11. C
N
O
Carbon(碳),Nitrogen(氮⽓), Oxygen(氧⽓)
Amino acid(氨基酸)
•Our body consists of protein(蛋⽩质) linked to amino
acid(氨基酸)
•The amino acid and protein consists of C,N,O etc
•These elements come from the stars
Let’s consider it more deeply
Human and elements
6
13. Types of matter
•We currently know of 118 different elements, ranging from the simplest hydrogen to
oganesson (Og)
118 protons and 176 neutrons
•The 81 stable elements found on earth make up the overwhelming bulk
of matter in the universe.
•In addition, 10 radioactive elements (e.g. radon and uranium) also
occur naturally on the earth.
•Furthermore, 19 more radioactive elements have been artificially produced under special
conditions in nuclear laboratories on the earth.
Natural radioactive elements: Stable (millions or even
billions of years)
Artificial radioactive elements: Not stable (less than
million years)
8
14. Abundance of matter
The cosmic abundance of the elements
•We can find the number of H and He is much larger than other elements.
•As we discuss in cosmology（宇宙学） part, hydrogen and helium formed in the early universe.
•On the other hand, other elements were formed by nuclear fusion in the core of stars.
9
15. Hydrogen and Helium burning
4 (
1
H) → 4
He + 2 positrons + 2 neutrinos + energy.
•Stellar nucleosynthesis begins with the proton-proton chain.
•4 protons form Helium and generate energy (and neutrinos)
as the result of nuclear fusion.
3 (
4
He) → 12
C + energy.
•As helium builds up in the core of stars, the burning
stops, and the core contracts and heats up.
•When the temperature exceeds about 100 million K,
helium starts fusion and generates carbon.
10
16. Carbon burning and helium capture
•At higher temperature, heavier elements are formed after carbon.
12
C + 12
C → 24
Mg + energy
But, this path is uncommon in stars because
the number of protons is rapidly increasing.
• Easier process occurs in stars to form heavier elements.
12
C + 4
He → 16
O + energy.
•At temperatures above 200 million K, carbon-
helium fusion occurs in the star and form oxygen.
11
17. Carbon burning and helium capture
16
O + 16
O → 32
S + energy.
•After oxygen is produced, sulfur(S) is generated
16
O + 4
He → 20
Ne + energy.
•It is much more probable that oxygen-16 nucleus will capture a helium-4 nucleus to
form neon-20.
12
C + 4
He → 16
O + energy. 16
O + 4
He → 20
Ne + energy.
•Now, we see that the following nuclei-reaction will easily occur in stars.
•It is common to capture helium-4 to form heavier elements (helium capture).
12
18. Carbon burning and helium capture
16
O + 16
O → 32
S + energy.
•After oxygen is produced, sulfur(S) is generated
16
O + 4
He → 20
Ne + energy.
•It is much more probable that oxygen-16 nucleus will capture a helium-4 nucleus to
form neon-20.
12
C + 4
He → 16
O + energy. 16
O + 4
He → 20
Ne + energy.
•Now, we see that the following nuclei-reaction will easily occur in stars.
•It is common to capture helium-4 to form heavier elements (helium capture).
12
19. Carbon burning and helium capture
16
O + 16
O → 32
S + energy.
•After oxygen is produced, sulfur(S) is generated
16
O + 4
He → 20
Ne + energy.
•It is much more probable that oxygen-16 nucleus will capture a helium-4 nucleus to
form neon-20.
12
C + 4
He → 16
O + energy. 16
O + 4
He → 20
Ne + energy.
•Now, we see that the following nuclei-reaction will easily occur in stars.
•It is common to capture helium-4 to form heavier elements (helium capture).
So, you may think that it is easier to form a mass of 4 units such as 12 units(C), 16 units(O),
20 units (Ne), 24 units (Mg), and 28 units (Si) by helium capture.
12
20. Carbon burning and helium capture
Yes, it is true!
We can see the peaks for these elements in cosmic abundance
13
21. Iron formation
•When silicon-28 (Si) is formed, the temperature of the core reaches 3 billion (30亿)K. Thus,
high-energy gamma-ray photons are generated. These gamma-ray photons break silicon
into Helium.
•By capturing these helium-4 nuclei, heavier elements are
formed (alpha process) until Nickel-56(Ni)
28
Si + 7 (
4
He) → 56
Ni + energy.
•But, because nickel-56 is unstable, it rapidly decays to iron-56 (Fe)
56
Ni → 56
Co → 56
Fe
14
22. Iron formation
•Iron (Fe) has the greatest nuclear binding energy. Thus, it is stable and needs more energy
to break into other elements.
The abundance of iron is higher than
other lighter elements.
15
23. Making elements beyond iron
•At the core of a star, the alpha
process stops at iron(Fe).
•But, we know there are much heavier
elements than iron such as gold(Ag)
and platinum(Pt).
How did heavier elements such as
gold and platinum form??
16
24. Making elements beyond iron
•Heavier than iron(Fe) is produced by neutron capture.
Fe
n
56
Fe + n → 57
Fe
57
Fe + n → 58
Fe .
58
Fe + n → 59
Fe .
By the way, there is a radioactive decay called “ ”
β − decay
n ⟶ p + e−
+ ν̄e
•Neutrons are transformed to proton with emitting
electron and neutrino
17
25. Making elements beyond iron
•When occurs in nuclei, the number of a
proton is increased and generates heavier elements.
β − decay
n ⟶ p + e−
+ ν̄e
•Remember what is the difference between iron (Fe) and cobalt-59 (Co).
26Fe 27Co
•The number of protons in Fe is 26 and the number of protons in Co is 27.
(e.g)
59
26Fe ⟶59
27 Co + e−
+ ν̄e
•Due to neutron capture and , heavier elements are generated.
β − decay
•If this process occurs slowly (~ 1000 years), it is called an “s(slow)-process”.
18
26. Making elements beyond iron
•The s-process can explain the synthesis of stable nuclei up to 209
83 Bi
•There must be yet another nuclear mechanism that produces the very heaviest nuclei.
These process is called “r(rapid)-process”
•Although the s-process takes time around ~1000 years, the r-process occurs within
a few minutes in stars.
•The r-process happens in a few minutes, thus we need to supply neutrons rapidly to
make the r-process happens.
It may occur when
neutron stars merge!
But, we have not observed the evidence of the
r-process until 2017…
19
27. Gravitational wave
•Not only electromagnetic waves but also gravitational waves had been detected by LIGO
and Virgo.
LIGO detectors
•We observed the gravitational wave from
merging black holes in 2015.
•Gravitational wave was predicted by
Einstein in 1915.
20
28. Gravitational wave
•Not only electromagnetic waves but also gravitational waves had been detected by LIGO
and Virgo.
LIGO detectors
•We observed the gravitational wave from
merging black holes in 2015.
•Gravitational wave was predicted by
Einstein in 1915.
20
29. Gravitational wave and multi-wave observations
•We observed the gravitational wave from merging neutron stars in 2017
•At the same time, we successfully observed these neutron stars by other wavelengths
of the electromagnetic wave (Optical, X-ray, Infrared, radio)
Gravitational wave
Electromagnetic wave
It is the first evidence of the r-process!
The beginning of multi-messenger astrophysics!
https://kilonova.org/p2
21
32. Summary
• Heavier elements lighter than Fe form by helium capture
inside stars.
• Heavier elements than Fe form by neutron-capture inside
stars (s-process, r-process)
• Recently, we have observed the evidence of the r-process
by gravitational wave and multi-wave observations.
24
