impact of magnetic field on circumstellar disk formation€¦ · disk formation is suppressed by...
TRANSCRIPT
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Impact of magnetic field on circumstellar
disk formation
Yusuke Tsukamoto (Kagoshima U)
Shuichiro Inutsuka, Masahiro MachidaKazunari Iwasaki, Satoshi Okuzumi
Hajime Susa, Hideko Nomura
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Outline
• Introduction
• Part1: Impact of dust size on formation and early evolution of YSOs with Ohmic and ambipolar diffusion (based on Tsukamoto+ submitted)
• Part2: Interplay of magnetic field-angular momentum misalignment of molecular cloud cores and Hall effect (based on Tsukamoto+17)
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Kwon+18
BISTRO
From filament to circumstellar disk
Cloud core
Molecular cloud
Cloud core
Andre+17Andre+17
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J flux
Magnetic field extracts angular
momentum from central
region→Magnetic braking
Disk formation is suppressed by
magnetic braking in idealized setup (ideal
MHD, coherent rotation, aligned B field)
→Magnetic braking catastrophe
(MBC;Mellon&Li+08)
落下速度Li+2011
vr
vφ
Radius
落下速度100 AU100 AU
Rotation stops
100AU
μ=5
μ=20
μ=100
Bate+ 14
Typical case
weak B field
strong B field
Magnetic braking and suppression of disk formation
Braiding+11
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Mechanisms to solve magnetic braking catastrophe
• Realistic effect weakens magnetic braking– Turbulence diffusion (Santos-Lima+12
→Reinaldo talk)– Non-ideal MHD effect
(Machida+11,Tsukamoto+15, Tomida+15)– Misalignment of B and J (Hennebelle+09,
Joos+12, Tsukamoto+17,18)
• Many observations already find disks!→MBC is essentially solved
• We investigate more specific questions:1. How dust growth affects formation and
evolution of YSOs?2. How non-ideal effects work in misaligned
cloud core?
Santos-Lima2012
Yen+17
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Part IImpact of dust size on formation and early evolution of circumstellar disk with Ohmic and ambipolar diffusion
Nakano+02
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Why dust for non-ideal effect?
• Magnetic resistivity (ηO, ηH
ηA) depends on ionization state
• Ionization state is mainly determined by dust size and CR ionization rate
→dust size distribution is crucial to quantify the impact of non-ideal effect
Nakano+ 02
Okuzumi+09
Hall effectAmbipolar
diffusion
Ohmic
diffusion
Nakano+02
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Ricci+10
Possible dust growth in the cloud core• Recent obs. suggest the dust growth
in very young YSOs– Dust size constraint from RAT theory
and polarized fraction (Valeska+19)– Optical index β decreases even in
Class 0 YSOs (Kwon+07)
• From theoretical point of view, dust can grow to <~1 μm in envelope and >>1 μm in disk of Class 0. (Hirashita+13)
Valeska+19
Hirashita+13
Kwon+07
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Dust size dependence of resistivity• By dust growth
– ηA decreases in disk , ηA increases in envelope
– ηO decreases both in disk and envelope
→Complex dependence on dust size may introduce diversity of dynamics
diskenvelope
ηA
increases
ηA ,ηO
decreases
Gas density
Solid:ηA
Dashed:ηO
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・μ=(M/Φ)/(M/Φ)crit~1
・r~104 AU
・B~10-5 G=10 μG
B
μfreeze~1
r~100 AU
⇒Bfreeze~ 100 mG
→β=0.1 !
• By dust growth, disk evolution is changed?
• Outflow evolution is changed?
• Magnetic flux accretion is changed?
– If all magnetic flux goes to disk, disk magnetic field is too large!
The questions addressed in this part
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Setup of 3D simulations• Init cond.:Bonnor-Ebert sphere
– M=1 Msun, (M/Phi)=4 for const B
• Non-ideal effect: Ohmic, ambipolardiffusion
• Calculated untill Mstar~0.1Msun (>104
yr after protostar formation • Parameter: dust size distribution
– ISM like dust model– Large dust model
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Time evolution of large dust model
Spiral arm formation by GI
1000AU 250AU
edgeon
faceon
Absence of outflow in early phase
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Time evolution of ISM dust model
Disk begins to shrink after warp formation
1000AU 250AU
edgeon
faceon
Warp formation in later phase
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Disk size evolution • Disk with large dust tends to be larger than with small dust
• Simulation results seems to consistent with disk size evolution of Class0 YSOs
■:Disk size from ALMA obs.
Fitting formula of Yen+17
Disk size evolution
Increases with dust size
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Disk mass evolution• Disk with large dust tends to have
spiral arms by GI→ can explain recent obs of HH111 (Lee+20) or Elias 2-27 (Pérez+16)⇔Compared to obs. of Class 0 YSOs, disk tends to factor of 2-3 massive.
Lee+20
■:Disk mass from ALMA obs.
Disk mass evolution
Lee+20
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Outflow evolution• The outflow mass decreases
as dust size increases• The outflow mass and
dynamical timescale are consistent with the observations of young outflow
Wu+04
Decreases with dust size
Outflow mass
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Outward B field drift• Ambipolar diffusion induces outward B field drift in envelope
• We find B field drift happens with relatively large grain in later phase (Mstar>0.1 Msun)
→magnetic flux accretion to disk decreases with large grain
→disk formation is enhanced Large dust causes outward radial drift
ss
H2
H2
H2 i+
e-
vdrift
vdrift
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Part II
• Interplay of magnetic field-angular momentum misalignment
and Hall effect (Tsukamoto+17)
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J_ang
Bθ
Hull+19
Hull+14
Relative angle of magnetic field direction and outflows
Galmetz+18
• Observations reveal misalignment between disk Jang and B is common– Bimodal θ for Class O YSOs– Random θ for low-mass protostellar cores
→Does misalignment change disk formation process?
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Previous studies with misaligned cloud cores(ideal MHD)• Hennebelle+09, Joos+12 with ideal MHD
simulations showed misalignment weakens magnetic braking (MB)
θ=0゜
θ=90゜Joos+12
Joos+12
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Previous studies with misaligned cloud cores(ideal MHD)
B
B
Small disk with θ=0 large disk with θ=90
Joos+12
• Hennebelle+09, Joos+12 with ideal MHD simulations showed misalignment weakens magnetic braking (MB)
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gas rotation induced by Hall effect• Hall effect induces the left-handed screw rotation
around the local magnetic field (JH : Purple arrow)
At midplane,
left-handed
screw rotation
is inducedBJH
toroidal current at midplane
→toroidal magnetic field
→toroidal magnetic tension
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Hall induced rotation in misaligned core• Jang is vector sum of initial Jang and Hall induced Jang
• Acute angle and obtuse angle cause different resultalthough it can not distinguish from polarized emission
B
Jini
Jini+JH
B
JiniJH
Jini+JH
JH
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Question for Part II:
How Hall effect modifies disk formation in misaligned core?
B
Jini
Jini+JH
B
JiniJH
Jini+JH
JH
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Simulaiton setup
Okuzumi+09
Simulations starting from cloud core
θ
• Init condition– M=1 Msun, (M/Phi)=4
• Non-ideal effect: Ohmic, ambipolar diffusion and Hal effect
• Calculated untill the protostarformation
• Parameter: relative angle between initial J and B
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Density structures with various θ
• pseudo-disk along B field direction (r~500AU) forms
800AU
Initial B direction
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200AU
Disk normal is neither parallel to B and initial J !
Disk size ↑ as θ ↑Intial B directionJ direction
Density structures with various θ
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• Jang(θ=0)< Jang(θ=90) < Jang(θ=180)
→Disk in parallel core can be larger or smaller than perpendicular (θ=0 and θ=180 are not distinguishable)
180deg=anti-parallel
90deg
=perpendicular
0deg= parallel
~1000AU ~100AU <=10AU
Angular momentum profile with Hall effect
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B
B
B small disk with θ=0
Medium sized disk with θ=90
large disk with θ=180
Angular momentum profile with Hall
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Observation of disk in parallel cores• Hall effect may assist disk and binary formation in
anti-parallel cloud core
→Kwon+19 pointed out that the relatively large disk (and binaries) can form even in parallel cloud cores
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Comparison between ηturb
with free-fall timescale
• In collapsing cloud core, turbulence is trans- to sub-sonic
vturb < cs < vff → vff /vturb>1• Comparison with free-fall timescale
(Magnetic Reynolds number)
Re =vffλJ
𝜂𝑅𝐷=
vff 𝜆𝐽𝑣𝑡𝑢𝑟𝑏𝜆𝐽
=𝑡difftff
> 1
ηRD = vturb 𝐿min 1,𝑣𝑡𝑢𝑟𝑏𝑣𝑎
𝑎
< 𝑣𝑡𝑢𝑟𝑏 𝐿
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Comarison between ηturb and ηO, ηA
ηturb=cs λJ
Zhao+ 18
ηturb=cs λJ
Important region is here!Lam+19 does not include this increase by dust
ηO ηA
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Summary
• Part I :– Disk size positively depends on
dust size
– Outflow mass negatively depends on dust size
– Outward magnetic field drift happens only with large dust grain
→Dust growth in star forming region changes disk evolution!
• Part II:– With Hall effect, central angular
momentum of acute/obtuse angle differs
→(Apparent) misalignment not always enhances the disk formaiton
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Backup slide
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Formation of warped pseudo-diskand negative impact on disk growth• The warp of pseudo-disk develops in ISM dust
models and not in large dust models• Due to the warp formation, the magnetic flux
tube contracts→magnetic field in the disk is enhanced→stronger magnetic braking →Disk begins to shrink
Flux tube contracts
Magnetic field increases
Disk begins to shrink
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中心角運動量の向き
ホールあり
ホールなし
180deg=anti-parallel135deg
90deg
0deg= parallel
45deg
70deg
110deg
90deg
0deg= parallel
45deg
70deg
• 中心領域の角運動量の向きは10-15<ρ<10-13で急激に変化
→中心付近(数100AUスケール)で回転がゆがんだ構造が実現
• 磁場/初期角運動量の向きと大きく異なる
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When Hall effect becomes important ?• Magnetic resistivity strongly depends on the CR
ionization rate and dust size• Koga+19 investigate how characteristic disk size by Hall
effect depends on grain size and CR ionization rate• Hall effect becomes important when
1. cosmic ray ionization rate is low (ζ<~10-17 s-1)2. dust grain is sub-micron (a~ 0.05 μm)3. Magnetic field is strong (μ~1)
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Turbulent diffusion rate
ηturb~𝑣𝑙 𝜆𝐽 ~1018
𝑣𝑙200 𝑚 𝑠−1
𝜌
10−13𝑔 𝑐𝑚−3
−12
𝑐𝑚2 𝑠−1