1. Introduction to modern astronomy18
島袋隼⼠(Hayato Shimabukuro)（云南⼤学、
SWIFAR）
©GETTYIMAGES
1

2. 11.Stellar explosions
（恒星爆发）
2

3. Life after death for white dwarf
•One type of star, called a nova, may increases enormously in brightness by a factor of
10,000 or more.
•After several months, the brightness gradually fades slowly back to normal.
3

4. Life after death for white dwarf
•We noted that the white-dwarf stages represents the end
point of star’s evolution.
•The stars gradually cools because its core are burned
out.
This scenario is quite correct for isolated star!
But, the situation is different in the
case of binary system!
4

5. Life after death for white dwarf
•We noted that the white-dwarf stages represents the end
point of star’s evolution.
•The stars gradually cools because its core are burned
out.
This scenario is quite correct for isolated star!
But, the situation is different in the
case of binary system!
4

6. Life after death for white dwarf
•The mass is transferred from main-sequence
companion to white dwarf.
•The transferred mass disk around white
dwarf is called accretion disk.
•Because of friction（摩擦）, the temperature of
accretion disk is high and it radiates X-ray.
5

7. Life after death for white dwarf
•The hot gas is built on the surface of white dwarf.
•Then, the hydrogen on the white dwarf’s surface
ignites, fusing into helium.
•The star suddenly flares up in luminosity and
then fades away as some of the fuel is
exhausted.
6

8. Life after death for white dwarf
7

9. Life after death for white dwarf
7

10. Life after death for white dwarf
(a)The ejection of material from a star’s surface
can clearly be seen.
(b) At left panel, more than a year after the
blast, a rapidly expanding bubble is seen.
(b) At right panel, 7 months after the right
panel. The shell continued to expand and
distort.
8

11. The end of high-mass star
•A low mass star ( )
≲ 8M⊙ C
It ends its life as a carbon-oxygen
white dwarf.
•A high mass star ( )
≳ 8M⊙
Even heavier elements are
produced in the core.
Fe
Can anything stop nuclear fusion process?
Is there a stable “White-dwarf-like” state at the end of
the evolution of high-mass star?
What is the ultimate fate of such a star? To answer these questions, we must look
more carefully at nuclear fusion in massive
stars.
9

12. Fusion of heavy elements
Core in high mass star
•In massive stars’ core, heavy elements are
synthesized to form layer structures.
•The nuclear fusion depletes the lighter elements
to create heavier elements, and the heavier
elements form the shell structure on the inside.
•The core itself is composed of iron.
This is key reaction in the heavy element
fusion chain.
10

13. Collapse of the iron core
The graph shows
mass per nuclear particle
.vs.
number of particles in nucleus
(Note)
(Mass per nuclear particle)=Mass/Y
Y
XA
(e.g.) 4
2He 12
6 C
•For example, Helium is more stable than Hydrogen. Thus, the mass is lost and energy is
released to form Helium by nuclear fusion.
Lower mass (energy) is stable!
11

14. Collapse of the iron core
The graph shows
mass per nuclear particle
.vs.
number of particles in nucleus
(Note)
(Mass per nuclear particle)=Mass/Y
Y
XA
(e.g.) 4
2He 12
6 C
Lower mass (energy) is stable!
•Elements to the left of iron release its energy through fusion reactions.
(e.g)
Energy
12

15. Collapse of the iron core
The graph shows
mass per nuclear particle
.vs.
number of particles in nucleus
(Note)
(Mass per nuclear particle)=Mass/Y
Y
XA
(e.g.) 4
2He 12
6 C
Lower mass (energy) is stable!
•Elements to the left of iron release its energy through fusion reactions.
(e.g)
Energy
12

16. Collapse of the iron core
The graph shows
mass per nuclear particle
.vs.
number of particles in nucleus
(Note)
(Mass per nuclear particle)=Mass/Y
Y
XA
(e.g.) 4
2He 12
6 C
(e.g)
13

17. Collapse of the iron core
The graph shows
mass per nuclear particle
.vs.
number of particles in nucleus
(Note)
(Mass per nuclear particle)=Mass/Y
Y
XA
(e.g.) 4
2He 12
6 C
•On the other hand, the elements to the right of iron
releases its energy by fission（裂变）.
(e.g)
13

18. Collapse of the iron core
The graph shows
mass per nuclear particle
.vs.
number of particles in nucleus
(Note)
(Mass per nuclear particle)=Mass/Y
Y
XA
(e.g.) 4
2He 12
6 C
•On the other hand, the elements to the right of iron
releases its energy by fission（裂变）.
(e.g)
13

19. Collapse of the iron core
The graph shows
mass per nuclear particle
.vs.
number of particles in nucleus
(Note)
(Mass per nuclear particle)=Mass/Y
Y
XA
(e.g.) 4
2He 12
6 C
•On the other hand, the elements to the right of iron
releases its energy by fission（裂变）.
(e.g)
13

20. Collapse of the iron core
The graph shows
mass per nuclear particle
.vs.
number of particles in nucleus
(Note)
(Mass per nuclear particle)=Mass/Y
Y
XA
(e.g.) 4
2He 12
6 C
•On the other hand, the elements to the right of iron
releases its energy by fission（裂变）.
(e.g)
•Most stable element is Iron.
13

21. Collapse of the iron core
•The core temperature rises to nearly 10 billion（100亿） K
•At such high temperature, photons have enough energy to split iron into lighter nuclei and
then to break those lighter nuclei apart until only protons and neutrons remain. (Photo
disintegration)
Fe
Fe ⟶ p, n, e
Photons
p + e → n + neutrino.
•Protons and electrons are crushed together, forming neutrons and neutrinos (neutronization )
in the core.
!
ρ ∼ 1012
kg/m3
14

22. Supernova explosion
p + e → n + neutrino.
•Because electrons disappear and neutrinos are emitted, there is
now nothing to prevent it from collapsing by gravitational
force.
gravity
!
ρ ∼ 1015
kg/m3
•The neutrons in the shrinking core offer rapidly increasing
pressure to prevent from gravitational collapse.
n
15

23. Supernova explosion
p + e → n + neutrino.
•However, gravitational collapse keeps going and the density of
the core becomes so large. Then, neutrons cannot shrink more.
Finally, the neutron core(it becomes a neutron star later)
forms.
!
ρ ∼ 1017−18
kg/m3
•The matter falls from the outside, strikes the neutron core, and
bounces off.
n
n
16

24. Supernova explosion
p + e → n + neutrino.
•However, gravitational collapse keeps going and the density of
the core becomes so large. Then, neutrons cannot shrink more.
Finally, the neutron core(it becomes a neutron star later)
forms.
!
ρ ∼ 1017−18
kg/m3
•The matter falls from the outside, strikes the neutron core, and
bounces off.
n
n
16

25. Supernova explosion
p + e → n + neutrino.
• When matters bounce off, shock wave is generated. This
shock wave blows away the gas in the star's layer
(Supernova explosion).
n
17

26. Supernova explosion
p + e → n + neutrino.
• When matters bounce off, shock wave is generated. This
shock wave blows away the gas in the star's layer
(Supernova explosion).
n
17

27. Supernova explosion
p + e → n + neutrino.
• When matters bounce off, shock wave is generated. This
shock wave blows away the gas in the star's layer
(Supernova explosion).
n
•Neutron core remains after star’s layer is blown away.
17

28. Supernova explosion
p + e → n + neutrino.
• When matters bounce off, shock wave is generated. This
shock wave blows away the gas in the star's layer
(Supernova explosion).
n
•This event is called core-collapse supernova.
•Neutron core remains after star’s layer is blown away.
17

29. Supernova explosion
18

30. Supernova explosion
18

31. Supernova explosion
SN1987A is a supernova which is discovered in Large Magellanic cloud
19

32. p + e → n + neutrino.
•(Super) Kamiokande detected neutrinos from
SN1987A
•This detection of neutrino help understand nuclear
fusion in the star’s core observationally.
•Masatoshi Koshiba won the Nobel prize for opening “Neutrino
astronomy”
20

33. 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)
21

34. 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
21

35. Type I supernovae
Type II supernovae
•There are two kinds of supernova.
Supernova（超新星）
22

36. Type I supernovae
Type II supernovae
•There are two kinds of supernova.
Low hydrogen
Lots of hydrogen
Supernova（超新星）
22

37. 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）
22

38. 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）
22

39. p + e → n + neutrino.
• When matters bounce off, shock wave is generated. This
shock wave blows away the gas in the star's layer
(Supernova explosion).
n
Type II Supernova
23

40. p + e → n + neutrino.
• When matters bounce off, shock wave is generated. This
shock wave blows away the gas in the star's layer
(Supernova explosion).
n
Type II Supernova
23

41. p + e → n + neutrino.
• When matters bounce off, shock wave is generated. This
shock wave blows away the gas in the star's layer
(Supernova explosion).
n
•Neutron core remains after star’s layer is blown away.
Type II Supernova
23

42. p + e → n + neutrino.
• When matters bounce off, shock wave is generated. This
shock wave blows away the gas in the star's layer
(Supernova explosion).
n
•This event is called core-collapse supernova.
•Neutron core remains after star’s layer is blown away.
Type II Supernova
23

43. p + e → n + neutrino.
• When matters bounce off, shock wave is generated. This
shock wave blows away the gas in the star's layer
(Supernova explosion).
n
•This event is called core-collapse supernova.
•Neutron core remains after star’s layer is blown away.
Type II Supernova
Type II supernova
23

44. Type I Supernova
24

45. Type I Supernova
•Type I supernova forms in binary stars.
24

46. Type I Supernova
•Type I supernova forms in binary stars.
•One of the binary pair stars becomes a white dwarf and the company star becomes a red-
giant star.
24

47. Type I Supernova
•Type I supernova forms in binary stars.
•One of the binary pair stars becomes a white dwarf and the company star becomes a red-
giant star.
•The white dwarf pulls gas from the red-giant star and makes an accretion disk around the
white dwarf.
24

48. Type I Supernova
•Type I supernova forms in binary stars.
•One of the binary pair stars becomes a white dwarf and the company star becomes a red-
giant star.
•White dwarfs usually have maximum mass (Chandrasekhar limit) and if the mass of a white
dwarf exceeds Chandrasekhar mass, it detonates
•The white dwarf pulls gas from the red-giant star and makes an accretion disk around the
white dwarf.
24

49. 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）
25

50. Supernova Remnants（超新星遗迹）
SN1054
Cassiopeia A
•We can observe supernova remnants as evidence of supernovae in our galaxy.
26

51. 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. 26