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What could Hinode results tell us about cosmic
magnetic fields?
1
Saku Tsuneta Institute of Space and Astronautical Science, JAXA
ISAS Astrophysics Colloquia 2015 February 26 11-12am
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EUV Imaging Spectrometer(EIS)
Solar Optical Telescope(SOT)
X-ray Telescope (XRT)
Japan-US-UK-ESA project Orbit: Polar Sun Synchronous Launched 2006 Autumn
Satellite Hinode (JAXA SOLAR-B)
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EUV Imaging Spectrometer(EIS)
Solar Optical Telescope(SOT)
X-ray Telescope (XRT)
Hinode mission objective: Systems approach to understand generation, transport and ultimate dissipation of solar magnetic fields with 3 well-coordinated advanced telescopes.
Japan-US-UK-ESA project Orbit: Polar Sun Synchronous Launched 2006 Autumn
Satellite Hinode (JAXA SOLAR-B)
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Too-strong Magnetic field in the Universe How does Universe create such strong fields?
• Early universe: 10-21G? • Galaxies and Clusters of Galaxy: 10-6 G • Late type stars 103G • Bottom of convection zone 105 G • Pulser 1012G • Magnetor 1015 G
4
Fossil or Compressive process? Dynamo? global dynamo? Local (turbulent) dynamo?
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Too-strong Magnetic field in the Universe How does Universe create such strong fields?
• Early universe: 10-21G? • Galaxies and Clusters of Galaxy: 10-6 G • Late type stars 103G • Bottom of convection zone 105 G • Pulser 1012G • Magnetor 1015 G
Fossil or Compressive process? Dynamo? global dynamo? Local (turbulent) dynamo?
Dynamo+? Dynamo+compression
Dynamo+?
Dynamo Compression and fossil?
needs dynamo
needs dynamo Compression and fossil
Any dynamo mechanism can amplify the magnetic fields upto equi-partition fields Be But not beyond! We sometimes need a mechanism to go beyond the equi-partition fields.
Kinetic Energy
Magnetic Energy
22
21
8ru
p»eB
5
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l 1.4 GHz
lVLA Galactic center Solar corona
Does nature prefer flux tubes? i.e. Does nature prefer higher magnetic energy state? 6
Courtesy of Sofue
NASA TRACE
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7
l 300 MHz
lStrong magnetic field of mG lMuch smaller than equi-partition field corresponding to the local gas lEquivalent to equi-partition field corresponding to galactic rotation (100-200 km/s)
Courtesy of Sofue
Galactic center:flux tubes? vertical to the G-plane
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9 Emer
genc
e of
mag
netic
fiel
ds
in a
form
of s
lend
er fl
ux tu
bes
With
B a
roun
d eq
ui-p
artit
ion
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Magnetic fields have a form of flux tube
Strong kG magnetic field in between convection cells exceeding equi- partition B
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11
1000km
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Hinode highest resolution Stokes-V map
(vertical component of B) Does nature prefer isolated flux tubes?
1000km
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Ishikawa+09
Distribution function of magnetic field strength
Peaks at 1.5kG Super-equipartition
majority:below500G Sub-equipartition
Two components
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Hinode result
Equi-partition field strength
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Sub-equipartition B 500G
Super-equipartition B 2000G 200 sec
Formation of super equipartition from sub-equipartition magnetic fields
Parker prediction:supersonic down flow associated with thermal instability results in compression of magnetic fields
Nagata+08
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Convection plus weak magnetic fields result in strong magnetic fields
Parker (1978); Hasan (1985), Hasan et al. (2003), Bunte, Hasan,Kalkofen, (1983)
G400421
82
2
»»
»
upr
rup
B
Be
kG218
2
-»
=+
B
PBP ei p
Magnetic Flux tube
Solar surface
Convection flow
Downflow Inside flux tube
15
15
Sub-equipartition B Super-equipartition B
Inhibit thermal energy due to B
Cooling and downflow
Stronger B due to lateral P balance
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Ishikawa+08
Convective collapse creates1.5kG flux tubes (This is not dynamo)
Convective collapse!! 500G 1.5kG Smaller total B energy
Larger total B energy
Peak at 1.5kG due to convective collapse
90% is below 500G Just born?
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Higher T.
Lower T.
Reduce heat Input from below
Lateral heat input from side
Slender flux tube
You are looking at deeper layer due to magnetic pressure
Dark sunspot and bright faculae
Emission From hot wall Solar surface is a
rias coastline due to thin flux tubes. It serves as heat sink.
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Same temperature
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Sun as seen in UV Bright faculae Dark sunpsot
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0.1-0.2%
Non-constant solar constant
Faculae (slender flux tubes win)!
Sola
r con
stan
t
year
amplitude of 0.1-0.2%
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Vertical magnetic flux Horizontal magnetic flux
Quiet Sun magnetic fields
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Ubiquitous linear polarization patches Lites+08, Orozco+07,08, Centeno+08 Ishikawa+08, 09, 10,11ab, Jin+09, Martınez Gonzalez+09 etc, Danilovic+10
Wherever convection, horizontal fields exist!?
250000km
120000km
Lites+08
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Local dynamo process discovered with Hinode
Ishikawa & Tsuneta (2008)
Total flux = 10-100 x sunspot Field strength < equi-partition Life time < granulation lifetime Size <granulation size
Horizontal B below equi-partition
Equi-partition field strength
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Discovery of New Dynamo Mechanism with Hinode
• Differential rotation of Sun amplifies magnetic
field 北極
南極
Magnetic field
Convection Energy
Magnetic Energy
北極
南極
北極
南極
Rotation Energy
Magnetic Energy
Convection cell 1000km Magnetic field
• Convection motion of plasma amplifies magnetic field
Sunspot Horizontal fields
Known mechanism Newly discovered
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2006 Dec 17 20:00-21:00 UT CaII H broad band filter images taken with Hinode/SOT
Chromosphere more dynamic than expected! Chromospheric jets and fountain
driven by magnetic force
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KM late type star: Fully convective Active corona Not consistent with Solar paradigm
Early type star: No convection zone No corona
Hayashi track: Proto star Convection dominant Active corona
Differential rotation driven global scale Dynamo and convection-driven dynamo
T tauri star: Convection Fast rotation Sunspot, wind Strong X-rays
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KM late type star: Fully convective Active corona Not consistent with Solar paradigm
Early type star: No convection zone No corona
Hayashi track: Proto star Convection dominant Active corona
Differential rotation driven global scale Dynamo and convection-driven dynamo
T tauri star: Convection Fast rotation Sunspot, wind Strong X-rays Convection
convection-driven local dynamo rotation⇒Reynolds stress ⇒differential rotation ⇒global dynamo
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Takeda & Takada-Hidai, PASJ (2011) • Subaru observations on 24
moderately to extremely metal-poor late type MS stars – Probably slowly or non-rotating
stars with global dynamo not operative
• HeI 1083nm detected for all stars – High excitation line (19.7 eV) – Excellent indicator for coronal
&chromospheric activities – He abundance independent of
metallicity • Nearly constant EW for all stars
– Corona exists regardless of metallicity (i.e. age, rotation period)
• Not driven by global dynamo
Sun
Extremely metal-poor
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Neutral universe with zero magnetic field due to zero electric current
First stars and re-ionization
B=1-30μG
B=0G
28 From website
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Conservation of magnetic flux
29
0)(0)0(
0
=FÞ==F
=F
ttDtD
How could we make such a strong magnetic fields currently observed?
Early universe present time
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)()(,0;0
)(
)(
;)0(
2
2
ttBBt
Be
Mce
pcvt
ven
pncBvtB
jenp
cBvE
e
e
ww
w
rrww
w
µ===
=
Ñ´Ñ-´´Ñ=
¶¶
´Ñ=
Ñ´Ñ-´´Ñ=
¶¶
=Ñ
-=´
+
じ;式が同じなら解も同
;渦度の誘導方程式
;渦度の定義
;誘導方程式
運動方程式
Sim
ilarit
y of
Indu
ctio
n eq
. an
d vo
rtex
eq.
30 R. Kulsrud, 2005, Plasma physics for astrophysics Princeton University Press
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Initial magnetic field strength after re-ionization epoch
• If baroclinic, vorticity exists and Biermann battery mechanism works, resulting in magnetic fields from zero value.
• How large is the magnetic fields? – r=100kpc, M=1011Mo – v=3x105 m/s(virial theorem) – ω~v/r=10-16 /s – B~10-20G!
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• Equi-partition field due to local dynamo OK! – n=10-3 cm-3
– v=3x105 m/s – T=100eV (106K)
• Maximum turnover time OK! – r/v=3x1023cm/3x107cm/s=1016s<<4x1017s (cosmic
life time) – Since actual Eddy size is smaller than the largest
scale size r taken here, this is a conservative estimate.
• A potential problem: not organized field
Turbulent dynamo then works to amplify the small magnetic fields to the current values
32
G108
5
22
-»
=
eq
eq
B
vB
rp
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宇宙は電離しておらず 電流なしのため磁場 ゼロ
第1世代銀河の形成 と宇宙の再電離
B=1μG
B=0G
33
Vortex in proto-galaxy produces magnetic fields as large as B=10-20G(Biermann Battery) ↓ Hinode: convection-driven dynamo amplifies B upto B=Beq=10-6G ↓ Global galactic dynamo B>10-6G
From website
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Galactic magnetic fields along spiral arms
• Highly organized • Observed magnetic
fields comparable to equi-partition field strength for local velocity dispersion
• Umag=B2/8π=U(ISM) • B=10μG
Courtesy of Sofue
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Discovery of transverse waves along magnetic field with Hinode (Okamoto et al 2008)
Spicules, coronal rains, and prominece over an active region 35
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Transverse Wave along magnetic field line carrying
substantial amount of energy
Alfven wave
Magnetic fields
gas
Figures Courtesy Joten Okamoto
Polarimetric data provides phase relationship among magnetic, velocity and intensity fluctuation, confirming transverse MHD waves (Fujimura, Tsuneta, 2009).
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In-Situ-like observations of MHD waves in solar photosphere
Field strength
Stokes-I Photometirc Intensity
Stokes-V • mode of waves • direction of wave • propagating or • standing waves • properties of flux • tubes
Observables: • δInteisnty(t) • δB / / (t), δB┴(t) • δVLOS(t) • center-to-limb var.
Doppler vel.
37
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Half of flux tubes show such clean common peak
Velocity Intensity Magnetic flux Ti
me
Prof
ile
Pow
er s
pect
ra
Fujimura&Tsuneta 09
Fujimura&Tsuneta 09
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Phase difference (deg) Phase difference (deg)
Phase difference (deg) Phase difference (deg)
φB-φV φV-φI(core)
φI(core)-φB φI(cont)-φI(core)
Fujimura&Tsuneta 09
--90deg --90deg
180deg -0 deg
-3-9min
Solid: pores+flux tubes
Dashed: pores
39
Velocity leads magnetic fields by quarter of waves.
Importance of phase relation to identify wave mode and direction of
propagation
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Discovery of Alfven waves from phase relation between δB and δ v, but almost
stationary waves!
δB- δ v:0 or 180 deg
δB- δ v:90 deg
Significant reflection of upward waves at photosphere-corona transition layer
Kink mode
Sausage mode
Fujimura&Tsuneta 09
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Residual Poyning Flux of kink wave Differential (upward – downward) Poynting flux is
proportional to cos(φB – φv)
An example with low intensity fluctuation (dI/I=0.3%)
f=0.73, B0=1.7x103 (G), δB=21(G), δv=0.059(km/ s), φB-φv=-96˚ giving ΔF=2.7x106 (erg/ s/ cm2)
f : average filling factor B0 : vertical magnetic field δB/ δv: root-mean-square transverse magnetic field/ velocity fluctuation
)cos(4 vBvBfBF ffddp
--=D
Fujimura&Tsuneta 09
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Sunspot number is a good proxy for magnetic activity of the Sun
11 year cycle of sunspot number from the era of Galileo
42
Year
Suns
pot n
umbe
r
Maunder minimum Dalton minimum
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Gradual decrease of solar activity Mean Sunspot number
1.0
0.0
-1.0 North
South
High latitude average magnetic flux Wilcox
Royal Belgium observatory
西暦
西暦 Reversal of high latitude field At around solar maximum 43
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Importance of polar fields to predict future solar activity (Choudhuri)
N
S
N
S
N
S
Cause Weak polar field
Result Less number of sunspots
130 rotations in 11 year
▽Ω-dynamo
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45 ひので
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西暦 西暦
Magnetic Flux (G)
Minus Plus
Minus Plus
Asymmetric north and south poles Still significant as of now
• Northern flux decreases rapidly • Southern flux has much slower decrease.
North South
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Quadruple poloidal fields (sketch)
Quadruple Bipolar 47
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N
S
N
N Bipolar mode Quadruple mode
Bipolar + Quadruple
Strong diffusion Weak diffusion
Sokoloff and Nesme-Ribes1994
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Anti-Joy’s law due to quadruple poloidal field
N N
N S
N S
Bipolar Sun Quadruple Sun
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Anti-Joy’s law AR#11429 signature of quadruple poloidal field?
50
N
N
S
S
N S
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1950-1990 (Recent normal cycle)
1670-1710 (Maunder minimum)
Smaller number of sunspots are located only in
Southern hemisphere
North
North
South
South
1680 1690 1700 1710 1720 1680
1950 1960 1970 1980 1990
Latit
ude
Latit
ude
+50
-50
Sokoloff and Nesme-Ribes1994
Location of sunspot emergence
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The dynamo equation
2015/2/26 52
[ ]
operation)in (dynamo )(1
)( Eq.induction ofcomponent
1
)( Eq.induction ofcomponent
22
22
ff
f
ffff
f
f
f
ah
h
BcEAr
rAr
vprt
ABBpoloidal
Brr
vrB
rB
vprt
B
BBtoroidalvvvBBB
ppp
p
p
p
p
p
=+úûù
êëé -Ñ=úû
ùêëé Ñ×+
¶
¶
Þ
úûù
êëé -Ñ+ú
û
ùêë
éÑ×=Ñ×+
¶¶
Þ
+=
+=
S
Bp
Ap On meridional plane: poloidal Perpen. to M.P.: toroidal
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One interpretation If cyclic phase differs between hemispheres,
Vector potential
Near-surface higher turbulent diffusivity
Hotta, Yokoyama, 2010 Fast meridional flow
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Cycle length: 12.6 year!
黒点数
西暦年
黒点数
Longer cycle period is also seen just before Dalton minimum
Dalton minimum
Year
Suns
pot n
umbe
r
Past 6 cycles (overlaid) Current cycle Northern hemispehre Southern hemisphere
Suns
pot n
umbe
r
NAOJ solar observatory
More anomaly of the Sun
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period~14yr
period~13yr period~12.6yr
Are we entering Maunder minimum?
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NS-asymmetry
N-S asymmetry?
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present
11400yr
4000yr
Sunspot number in the past 11400 years 56
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“Sports on a Frozen River” by Aert van der Neer Courtesy: The Metropolitan Museum of Art
The Maunder minimum
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Rotation
Turbulence
⇒ Differential rotation
Solitary star like the sun has strong magnetic fields!
⇒Local dynamo
⇒ Global dynamo
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Role of Magnetic fields in Stars and Cosmos and Hinode
• Carry energy through waves • Store energy • Dissipate stored energy with magnetic
reconnection • Induce MHD instability and eruptions • Suppress cross-field transport for mass
and heat • Suppress convection i.e. energy transport
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