Sec on 9.
Stellar stability and supernovae
9.1 Thermonuclear supernova

ti

9.2 Core-collapse supernova

Let’s understand these ques ons
with the words of physics• Why are stars so luminous?
• Why do stars show L ~ M ?
• Why do stars evolve?
• Why does the des ny of stars depend on the mass?
• Why do some stars explode?
• Why don’t normal star explode?
• Why does stellar core collapses?
• Why is the energy of supernova so huge?
•…
titi4

Binary system

White dwarf

David A. Hardy

Thermonuclear explosionCSiOFeSupernova!

Mass frac on

Explosion of white dwarf

CenterSurfacetiNomoto+84, Timmes+

Pre-explosion

Post-explosion

C+O
0.5

11.0

2
0.5

1.4

3

4

1.0

1.4

*NSE = nuclear sta s cal equilibrium (核統計平衡)
Ρ (g cm-3)

1(7-9) x 109

108-9

NSE + e-capture

56Fe, 54Fe, 58Ni

2(5-7) x 109

107-8

NSE

56Ni

3(4-5) x 109

<107

4

< 4 x 109

<107tiT (K)tizoneElements

Incomplete Si
burning
Incomplete O
burning

28Si, 32S, 40Ca
16O, 24Mg

Thermonuclear supernovae

Normal stars are stable with nuclear burning
Why do white dwarfs explode by nuclear burning?

Type IaSNSun0.0 sec

1,000 km

0.6 sec

2,000 km

3.0 sec
20,000 km

Roepke 2007

1.0 sec
70,000 km

How to trigger explosion (progenitor scenarios)
Accre on fromnon degenerate star

C: David Hardy

single degenerate

Merger of two white dwarfs

C: NASA

double degeneratetiWhich is correct or dominant? Not yet understoodSummary: Thermonuclear supernovae• Explosion of white dwarf close to Mch• Nuclear burning => runaway under degenerate condi on• Explosive nucleosynthesis• About 0.8 Msun of Fe-group elements ( Ni & Fe, Fe, Ni)
56

56

5458

> Core-collapse SNe• About 0.4 Msun of intermediate mass elements ( Si, S, Ca)28• Progenitor scenarioti• Single degenerate or double degenerate• Not yet solved

3240

Sec on 9.
Stellar stability and supernovae
9.1 Thermonuclear supernova

ti

9.2 Core-collapse supernova

M惑星状星雲> 10 Msun

1. Massive stars
軽い星

赤色巨星

~ 10 Myr

図の大きさは天体の大きさと一致していません(C: Essay Web)

白色矮星

HHeFeSiC+ONe + Mg

Images are not to scale20 Msun star（~16 Msun before the collapse)

Mass(Msun)

R(Rsun)Free-fall me(s)

16

1000

3x 107(1yr)

60.5

300

542
1.5

0.2

50
20
10.1

H
He
C/O
O/Mg
Si0.080.005
0.003

FeRsun = 7 x 1010 cm

tiR(Fe core) ~ 0.003 x 7 x 1010 cm~ 2 x 108 cm ~ 2,000 km

1000
HHe

0.5

Rho-T diagram

dege
nerat
ee

lec

trons

relativistic electrons

textbook by Polshen the temperature in the contracting C-O core reaches 5 − 8 × 108 K (depending on the mascore), carbon is the first nuclear fuel to be ignited. The reactions involved in carbon burning
fornuclear
burningstagestherTimescales
nuclear burning
cycleswere treatedin Sec.
6.4.3. In the following sections we briefly rev
se and discuss the consequences for the structure and evolution of the star. A typical example
interior evolution is shown in Fig. 12.7 for a 15 M# star, and the corresponding stellar proper
given in Table 12.1.

Table 12.1. Properties of nuclear burning stages in a 15 M# star (from Woosley et al. 2002).
burning stage

T (109 K)

ρ (g/cm3 )fuelmain products

timescalehydrogenheliumcarbonneon
oxygensilicon

0.035
0.18
0.83
1.6
1.9
3.3

5.8
1.4 × 103
2.4 × 105
7.2 × 106
6.7 × 106
4.3 × 107

HHeCNeO, Mg
Si, SHe
C, OO, Ne
O, Mg
Si, S
Fe, Ni

1.1 × 107 yr
2.0 × 106 yr
2.0 × 103 yr
0.7 yr
2.6 yr
18 d182

Neutron starorBlack hole

Collapse(< 1 sec)

Supernova!

Core-collapse supernovae

What happens to massive stars at the end of lives?
Where does huge energy come from?

ν(1)

(2)

Neutrino trapping

Core-collapseν

eFeνν ννFe coreννν	ShockSN neutrinoν"νν ννν ννν νν
ν νν

ν
(3)

νCore bounce
図 1.4

(4)

(5)

Supernova

Neutron star(C) 原子核から読み解く超新星爆発の世界

重力崩壊型超新星の爆発メカニズムの概要．重い星の中心部にある鉄住吉光介さん著 (Kosuke Sumiyoshi)
コアの重力崩壊から始まり，密度・温度が高まる中で発生したニューSummary: Core-collapse supernovae• Stability of star
• Dynamically unstable if adiaba c index γ < 4/3• Degenerate Fe core => unstable• What trigger the core-collapse?
• Energy source• Gravita onal energy• Collapse of the core (~1 Msun) to ~10 km sizetiti=> 1053 erg