Stellar Astrophysics I
恒星物理学特論 I
Masaomi Tanaka
田中 雅臣

Masaomi Tanaka (田中 雅臣)
h ps://www.astr.tohoku.ac.jp/~masaomi.tanaka/

Research topics- Time-domain astronomy- Transients (e.g., supernovae,neutron star mergers)

Observa ons- Wide eld survey (Subaru, Kiso)- Spectroscopy and spectro-polarimetry

Theorytitifititt- Radia ve transfer simula ons

Born in Nagoya (Aichi)
Grew up in Chita peninsula
2001-2009: U. Tokyo
2009: PhD at Univ. of Tokyo
2009-2011: Kavli IPMU
2011-2018: NAOJ
2018-now: Tohoku Univ.

Supernova

Research interests- Supernovae- Neutron star merger(gravita onal wave source)- Anything variable on the sky

Why do we study transients?
- Extreme physical condi on- End point of stellar evolu on- Origin of the elements- Many unsolved mystery

titi

titi

“ me-domain astronomy”

Neutron star merger

Elements around us
Air
Argon (Ar) 1.3 %CO2 0.05 %Neon (Ne) 0.001 %Oxygen (O)23%
Nitrogen (N)76%ti* Mass ra o (dry air)Our body
Ca 1.5%

P 1%

N 3%

Hydrogen (H)10%

Carbon (C)18%

Oxygen (O)65%

S 0.25%
K 0.20%Na 0.15%
Cl 0.15 %Mg 0.05 %The earth (crust)
Na 2%
Ca 3%

K 2%
Mg 1.5%

Fe 4%

Aluminum (Al)8%

Silicon (Si)30%

Oxygen (O)48%ti* Mass ra oThe beginningof the Universe
H, He, Li

C: Rhys Taylor, Cardiff University(Planck mission)Now
137 億年(13.7 billion yr )Our Universe“Heavy elements”
2%

O 0.6%
C 0.2%
Ne 0.1%
Fe 0.1 %Helium (He)25%

Hydrogen (H)73%ti*Mass ra oElement abundances in the Universe
1012

He10C1010810610410210010-2OFe

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
Atomic number Z*Mass ra oti

12Mass fraction (H=10 )HGoals of this lecture• Standard proper es of stars• Stellar structure and proper es• Stellar evolu on• Origin of the elements in the Universe• Nucleosynthesis in stars and supernovae• Explosion mechanism of supernovae• Topics in me-domain astronomy• Radia on from explosive phenomena• Mul -messenger astronomy
tititititititi

Minimum required knowledge for galac c astronomy

Course material and schedule
h ps://www.astr.tohoku.ac.jp/~masaomi.tanaka/tohoku2022* ~70% blackboard~30% slides

Contents • Overview• Stellar structure and proper es• Stellar evolu on• Supernovae• Origin of the elements and chemical evolu on of the Universe
Credit• Assignments / レポート課題

titititt

成績A few rules about this lecture• Please try order es ma on by yourself• This is essen al for astrophysics• Please ask ques ons• Your ques ons certainly help others’ understanding(you can ask ques ons in Japanese)• Please relax and enjoytitititi

fftiti• You can bring co ee/tea or chocolates/cookies, …

Sec on 1.
Overview: Life of stars, supernovae,
and origin of the elements
1.1 Stellar lives and supernovaeti

1.2 Origin of the elements

Our sun
Luminosity = 4 x 1033 erg/s(C) JAXA/ISAS

Japanese energy consump on (1 yr) = 2 x 1019 J = 2 x 1026 erg
Japan 107 yr = Sun 1 secti

How is this possible??

Energy source
A. Chemical reac on

B. Nuclear reac on

https://www.britannica.com/science/chemical-reaction(ex.) C＋ O2 -> CO2
Reac on of atoms/molecules= No change in nucleus(ex.) H + H + H + H -> HeChange in nucleus= Produc on of new elements

titi

ti

ti

Solar luminosity for 1010 yr
Really??

Stellar life

Why do stars evolve with me??

ti(C: Essay Web)

Hertzsprung-Russel diagram
Luminosity
Red giantsMainsequence

White dwarfs

Temperature (K)tth p://astronomy.nmsu.edu/geas/lectures/lecture23/slide04.html

Mass - luminosity rela on of the main sequence stars
6Star with M = 10 Msun=>1.0L ~ 104 Lsun=> Life me~ 1/103 of the Sun
0.5~ 1010 yr (100億年)/1034log (R / Rsun)log (L / Lsun)

L ~ M420~ 107 yr (1000万年)

0.0−0.5

More massive stars
have shorter life me−2−10log (M / Msun)

1−1.0−1Why??

0log (M / Msun)

tititi

Lectureby Pols of doubleFigure 1.3. Mass-luminosity (left) and mass-radius (right) relations
forNotecomponents

Applica ons to galaxy studies
Spiral galaxyEllip cal galaxy

M101

ESO 325-G004(C) NASA, ESAtititititi- Star forming- More “young" stars- More massive stars- Blue (high T radia on)- No star forma on- Old stars- Less massive stars- Red (low T radia on)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

HHeFeSi

C+O

Ne + Mg

Images are not to scaleNeutron starorBlack holeCollapse(< 1 sec)

Supernova!
Why?? How is this possible?

1-10 Gyr
赤色超巨星
重い星
2.
Low-mass stars

図の大きさは天体の大きさと一致していません(C: Essay Web)

超新星爆発
中性子星
M < 10 Msunブラックホール

HImages are not to scale

HeC+O

White dwarf

C+OWhy??
Low mass stars cannot make Fe?

Binary system

White dwarf

David A. Hardy

Thermonuclear explosion

CSiO

FeSupernova!
Why?? Normal stars do not explode with nuclear burning!

Progenitor
Elements

Core-collapse SNe

Thermonuclear SNe

Massive stars
Short life me

Low-mass stars (in binary)Long life meO, Mg, Ca, …
(progenitor star)

Si, Ca, Fe, …
(explosion)

titi

The elements around us are made by stars and SNeThe origin of elements
Big bang
Stars and supernovae

NhMc

Ts Og

Crab Nebula = M1

NASA/HST1572
Tycho Brahe“Stella Nova”
1604
Johannes Kepler“Astronomie+Populaire”++
by+Camille+Flammarion+(Paris,+1884)

Historical supernovaeName
SN 185SN 1006
CrabSN 1181
TychoKepler
SN 1987A

Loca onGalac cGalac cGalac cGalac cGalac cGalac c
LMC

Year
185
1006
1054
1181
1572
1604
1987

Magnitude-8?
-9?
-4?
0-4-3
3tititititititi~ 1 supernova every 100-200 yearsB. J. Fulton

SDSSHistory of SN discovery

fttth p://pro imobrien.com/2014/02/supernova-2014j-in-m82/

Light curve of supernovae(brightness as a func on of me)-20

Type Ia
Type Ib and Ic
Type II1043 erg s-1

Why soluminous??

-14-12

-10
0

50

100
150
200
250
Days after the explosion
ti

1041

-16

ti

1042

Absolute magnitude-18300350

Let’s feel SN explosion
Tycho’s supernova
Q. What is the average
Velocity of SN?

R ~ 1019 cm（10 light year ~3 pc）
Observed by Tycho Brahe in 1572
(Type Ia)

Velocity = Distance/ me
Distance: 1019 cm
Time: ~400 years
Velocity = 1019 / (400 x 3 x 107)
~ 109 cm/s ~ 10,000 km/s
10 light year = 10 year with light speed
SN takes 400 year to expand
Velocity = c/40= (300,000 km/s) / 40

ti

~10,000 km/s！

10,000 km

1
2
E = Mv
2Q. How large is the kine c energy?

Msun = 2 x 1033 g

Ekin ＝ 1/2 x Mass x (Velocity)2＝1/2 x (2 x 1033 g) x (109 cm/s)2~ 1051 erg

ti

Where does this huge energy come from?

Sec on 1.
Overview: Life of stars, supernovae,and origin of the elements
1.1 Stellar lives and supernovaeti

1.2 Origin of the elements

Cosmic abundances (atomic number)

1012

He

10C

10108106104

102

100

10-2O

Fe0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
Atomic number Z*Mass ra oti

12Mass fraction (H=10 )H

Cosmic abundance (mass number)
100-1

H He-2

O

1010C-310Fe-4

質量割合

10-510sプロセス

10-7Sr-610sプロセス

Ba-810Mass frac onrプロセス-9rプロセスsプロセス

Au PbPt

1010-10ti10-11050100
150
200
質量数 Mass number250

Our understanding about thenucleosynthesis is correct??

Chemical evolu on of the Universe
FeCore-collapse SNeMg

Thermonuclear SNeTime
109 yr 1010 yr
Core-collapse SNeTimetiti

Stars formed recently should have low Mg/Fe ra os

Stars keep informa on
about nucleosynthesis in the past
“Galac c archeology”

Our Galaxy

tititth p://astronomy.swin.edu.au/cms/astro/cosmos/T/Thick+Disk

[ Mg/Fnature and extent of n-capture nucleosynthesis in the early Galaxy. Abundance signatures of these0.5
elements can help to identify the parameters of the first stars—long since gone—and the sites forr- and s-process nucleosynthesis (Cowan & Sneden 2006). There are many ways to approach this0issue. We
begin in Figure 14 by contrasting the abundance behavior as a function of metallicityof the α element Mg and the n-capture element Eu. Only large stellar samples are employed forthese –0.5
correlations; the literature sources are listed in the figure caption.

Abundance ra o in Galac c stars (Mg/Fe)
ab[ Mg/Fe][Eu/Fe]1.5
1.5

100 MyrCore-collapse

Halo

1.0
1.0Disk1 Gyr10 Gyrthermonuclear

0.5
0.500
–0.5
–0.5

b1.5

–3

–2–10

[Fe/H]

Figure 14
Sneden+08
1.0[Mg/Fe] and [Eu/Fe] abundances as a function of [Fe/H] metallicity for halo and disk stars. For this figure
the data have been taken only from large-sample surveys: Fulbright (2000); Reddy et al. (2003); Cayrel et al.
(2004);0.5Cohen et al. (2004); Simmerer et al. (2004); Barklem et al. (2005, red points); Reddy, Lambert &Allende Prieto (2006); François et al. (2007). In both panels the dotted lines represent the Solar abundance
ratios. In panel b, the solid red line is a least-square fit to the Eu data, and the two dashed black lines indicate0
the approximate extent of the Eu/Fe data (similar to Cowan & Thielemann 2004).

[Eu/Fe]Timetititi

Longer delay me for Type Ia SNeSummary• Stars synthesize heavy elements• Stars evolve with me• Core-collapse supernovae• Origin of the elements such as Oxygen and Magnesium• Thermonuclear supernovae• Origin of Fe-peak elements• Supernova explosions• V ~ 10,000 km/s
• Ekin ~10 erg (10 J) => Feedback to galaxy forma on• Stellar nucleosynthesis is imprinted in Galac c starsti

44titi51

Let’s understand these ques ons
Knowing = Understanding
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

3 steps of learning
Short-term memory

1. Know
Have informa on<= Google is much be er
than we are!!

- L ~ M4

2. Connect with other knowledge
Long-term memory
Integrate knowledge, put it in some contexts- Massive stars have shorter life me- Physics behind it (radia on energy/di usion me)

3. Use the knowledge
Apply to other cases- Use galaxy color as indicator of star forma on- radia on energy/di usion me => L vs M of other systems=> understandtiti

fftitititt

fftititi“make it s ck - The Science of Successful Learning” Brown et al. 2016

Thermodynamics

Electromagne sm

Classical
mechanics

Sta s calmechanics

Astrophysics
Hydrodynamics

titititi

Rela vity

Quantummechanics
Nuclear physics