masahiro machida (kyoto univ.) shu-ichiro inutsuka (kyoto univ.), tomoaki matsumoto (hosei univ.)
DESCRIPTION
Protostellar Jet in the Collapsing Cloud Core. jet. Outflow. 360 AU. 1000 times close-up. Masahiro Machida (Kyoto Univ.) Shu-ichiro Inutsuka (Kyoto Univ.), Tomoaki Matsumoto (Hosei Univ.). first core. protostar. v ~5 km/s. v ~50 km/s. Star Formation and Jet / Outflow. - PowerPoint PPT PresentationTRANSCRIPT
Masahiro Machida (Kyoto Univ.) Shu-ichiro Inutsuka (Kyoto Univ.), Tomoaki Matsumoto (Hosei Univ.)
Outflow jet
first core protostar
v~5 km/s v~50 km/s
360 A
U
Protostellar Jet in the Protostellar Jet in the Collapsing Cloud CoreCollapsing Cloud Core
1000 times clo
se-up
?Star Formation and Jet / Outflow
Before the star formation Just after the star formation
Molecular Cloud Core Hirano et al. (2006)Jet from protostar
Stars born in the molecular cloud core
Jet / Outflow always appears in the star formation process
Jet / Outflow plays crucial roles in the star formation
They are closely related to the stellar mass
They transport the angular momentum from the cloud core
・・・・
(Nagoya Univ.)
We cannot observe
Jet /outflow driving phase
Protostellar Outflows and Jets
Velusamy et al. 2007
In star-forming regions, there are two distinct flows: Outflows and Jets
◆Molecular Outflow : low velocity (~10 km/s), wide opening angle
◆Optical Jet: high velocity (~100 km/s), well-collimated structure
Optical Jet is enclosed by Molecular Outflow
But, Mechanism is still unknown outflow
jet
protostella
r disk
Protostar
outflow
jet
dark cloud
protostar
Purpose of This StudyUnderstanding the driving mechanism of Jets / Outflows
Using the numerical simulation, we calculated the cloud evolution from the molecular cloud (n=104 cm-3, r~104 AU) until the protostar (n~1020 cm-3, r ~ 1Rsun) formation
HH30, Pety et al. 2006
Dead regionB dissipation(1012cm-3<n<1015cm-3)
B amplification B amplification
B BB
Lo
g T
(K
)
Log n (cm-3)
1010 1015 1020105
10
102
103
104
Isothermal Phase Adiabatic Phase Second Collapse & Protostellar Phases
Adiabatic core(First core)Formation
H2 dissociation
To MS
protostarformation
Gas Temperature
1D Radiative Hydrodynamics
Spatial Scale (AU)
104 100 1 0.1
Larson (1969)Tohline (1982)Masunaga & Inutsuka (2000)
cloud core
Thermal Evolution in the Collapsing CloudProtostar
Magnetic EvolutionR
esis
tivi
ty
Mag
netic R
eyno
lds n
um
ber : resistivity
v: free fall velocityL: Jeans Length
◆ Magnetic Reynolds number
L
R Me
v,
Ohmic dissipation
Well-Coupled Well-Coupled
◆ Resistivity is fitted as a function of n and T
(Nakano et al. 2002)
Coupling between the magnetic field and neutral gas (weakly-ionized plasma)
Low density (n<1012 cm-3): Low ionization rate, but well-coupled due to ff > col
Moderate density (1012cm-3<n < 1016cm-3) : Ionization rate decreases as density increases ⇒ Dissipation of B by Ohmic dissipation
High density (n>1016 cm-3) : Some metals are ionized, Well-coupled
Resistivity
Reynolds number Re
Cloud ProtostarCloud evolutionCloud evolution
B B
B
◆Basic equations
),( Tn
Gas sphere in hydrostatic equilibrium Critical Bonner-Ebert Sphere
+ Rotation + Magnetic Field
Magnetic field lines are parallel to the rotation axis: B//
Parameters: α, ω
α=Bc2/(4cs) :magnetic field strength
(ratio of the magnetic to thermal pressure)
=/(4G)1/2 : angular velocity normalized by freefall timescale
Initial ValueNumber density : n=104 cm-3
Temperature : T=10K
Bonnor-Ebert Sphere
Rotation Axis
Mag
net
ic F
ield
Lin
e
Ω
B
4.6x104 AU
L=4
(Bx,0, By,0, Bz,0) = (0, 0, (4cs)1/2 )
(x,0, y,0, z,0) = (0, 0, (4G)1/2 )
Cloud scale: 4.6x104 AU
Mass : Mtot =14 Msun
Initial Settings
同時刻、異なるグリッドスケール
L = 1
L = 2L = 3
L = 31L=4
Schematic view of Nested Grid
At the same epoch but different spatial scales
Example of Nested Grid
3D Resistive MHD Nested Grid Method Grid size: 128 x 128 x 64 (z-mirror sym.) Grid level: lmax=31 (l : Grid Level) Total grid number: 128 x 128 x 64 x 31
For uniform grid, (128x2x1030)x(128x2x1030)x(64x2x1030)
~ (1030)3 cells are necessaryGrid generation: Jeans Condition
l =1: Lbox = 4 pc, n = 103 cm-3 (initial)l =31: Lbox = 0.2 Rsun, n = 1023 cm-3 (final)
10 orders of magnitude in spatial scale 20 orders of magnitude in density contrast
Numerical Methods
Cloud Evolution from Molecular Cloud to Protostar
nc=104 cm-3 nc=109 cm-3 nc=1011 cm-3 nc=1013 cm-3
nc=1015 cm-3 nc=1017 cm-3 nc=1021 cm-3 nc=1022 cm-3
Initial State Isothermal Collapse
First Core Formation
Adiabatic Collapse
Outflow Driving
Magnetic Dissipation
Second Collapse
Protostar & Jet
n= ~5x10n= ~5x101111 cm cm-3-3 :First core formation, B field begins to be twisted
101011 11 cmcm-3-3 <n< 10 <n< 1013 13 cmcm-3-3 : B field strongly twisted, outflow appears
101013 13 cmcm-3-3 <n< 10 <n< 1016 16 cmcm-3-3 : B Field is dissipated by the Ohmic dissipation (Br, B) The magnetic field lines are uncoiled (Bz becomes major component⇒ )
101016 16 cmcm-3-3 <n< 10 <n< 1020 20 cmcm-3 -3 : Second collapse, B is coupled with the neutral gas, amplified again
n>10n>1020 20 cmcm-3-3 : Protostar formation, Br, Bincrease again
100
AU
Evolution of the Magnetic field at center of the cloud
Grid level L =14 (Side on view)Magnetic flux against the central density
Magnetic flux is largely removed from the first core for 1012-1016 cm-3
Ideal MHD model
Resistive MHD model
Dissipation by the Ohmic Dissipation
Low-velocity Flow from First core High-velocity flow from Protostar
~1
00
0 tim
es
c
los
e-
up
of th
e c
en
tral a
rea
360 AU 0.35 AU
First Core : n~1011 cm-3, r~10-100 AU
Protostar : n~1021 cm-3, r~0.01 AU
Outflow and Jet Driving Phase
voutflow~ 5 km/s vJet~50 km/s
Two distinct flows appear in the collapsing cloud!!
L=12 L=22
Adiabatic core (first and protostar core) formation ⇒ rot < collapse
Magnetic field lines are twisted ⇒ ⇒ Flow driving
Each core has different scale and different magnetic field strength
First Core does not experience the Ohmic dissipation: Strong field, hourglass
Protostar experiences the Ohmic dissipation: Weak field, straight lines
Driving Phase of Each Flow
1000 times close-up
103-105 yr
Different degrees of the collimation are caused by different driving mechanisms
Around First Core (Outflow) Lorenz Centrifugal Thermal Pressure ≒ ≒ (inflow)
Around Protostar (Jet) Centrifugal Thermal Pressure >> ≒ Lorentz (inflow)
Magnetocentrifugal wind First core, Outflow⇒
Driving Mechanism
Magnetic pressure gradient wind + MRI ⇒ Protostar, Jet
Disk Wind
Strong B
Wide Opening Angle
B gradient
Weak B
Narrow Opening Angle
・ Strong B・ flow along B lines・ hourglass B
・ weak B・ Flow along rotation axis・ straight B
Collimation
~1-10 >1000
First Core Protostar
Forces
Flow speed is determined by gravitational potential of each core (Kepler speed)
First core: ~0.01 Msun, ~1 AU v⇒ Kep~ 5 km/s ⇔ vmax= 5 km/s (simulation)
Protostar: ~0.01 Msun, ~1 Rsun v⇒ Kep~50 km/s ⇔ vmax= 50 km/s (simulation)
We calculated the very early phase of the star formation
Flow speeds increases with core mass
The Kepler speed is proportional to M∝ 1/2
When the first core and protostar grow up to ~1Msun
Outflow v⇒ Kep~ 50 km/s
Jet v⇒ Kep~500 km/s
Flow Speed
20 AU
First core
Proto star
Driver Speed collimation Mechanism Configuration of B
Outflow First core Slow (~10km/s) △ Disk Wind Hourglass
Jet Protostar High (~100km/s) ◎ Mag. pressure Straight
Our simulation could naturally reproduce properties of outflows and jets
Properties of Outflow and Jet
Schematic View
Low-velocity outflow is enclosed by the high-velocity Jet
Summary To avoid artificial settings around the protostar, we calculated the cloud evolution (or jet driving) from the molecular cloud (n=104 cm-3) until the protostar formation (n~1023 cm-3)
Outflow is directly driven from the first core (not entrainmented by jet)
Two distinct flows: Outflow from the first core, Jet from the protostar
Outflow: wide opening angle and slow speed
Jet: well-collimated structure and high speed
The differences between outflow and jet is caused by different strength of magnetic field, and different depth of gravitational potential
Different strength of magnetic field is caused by the Ohmic dissipation
Deferent depth of the gravitational potential is cause by the thermal evolution of the collapsing cloud
10000 AU
Outflow driving point (small scale)
Outflow propagation (middle scale)
Velusamy et al. (2007) HH47
Interaction between outflow and molecular cloud
Interaction between outflow and host cloud (large scale)
500 AU
8000 AU
2000 AU Initial Molecular Cloud CoreBow shock, Cavity,
Turbulence
unsteady