1. Protostellar jets: Theory & models Fabien CASSE Fabien CASSE AstroParticule & Cosmologie (APC) Université PARIS DIDEROT

2. Seminaire MHD, ENS Paris, 25/09/06 2 Outline of this talk  Observational facts. Young stellar objects (YSO), microquasars, active galactic nuclei (AGN) and related outflows: Young stellar objects (YSO), microquasars, active galactic nuclei (AGN) and related outflows: What do we know about them ?  Accretion disks and jets.  Interplay between disk-driven jets and stellar winds.  Concluding remarks.

3. Seminaire MHD, ENS Paris, 25/09/06 3 Young stellar objects  YSO (M * ≤ 2 M o ) exhibit large scale jets V jet ~ 100 - 400 km/s V jet ~ 100 - 400 km/s Jet rotation ( Baciotti et al. (2003)). Jet rotation ( Baciotti et al. (2003)). Jet velocity decreases with radius. Jet velocity decreases with radius. Presence of magnetic field Donati et al(2005). Presence of magnetic field Donati et al(2005). YSO jets seem to have 2 components (central one is hot, external one is cooler and more extended, Dupree et al (2005)). YSO jets seem to have 2 components (central one is hot, external one is cooler and more extended, Dupree et al (2005)).  Jet and disk luminosities seem related Burrows et al.(1996 ) Cabrit et al(1990)

4. Seminaire MHD, ENS Paris, 25/09/06 4Microquasars  Binary compact objects surrounded by an accretion disk. V jet ~0.1 to 0.95c V jet ~0.1 to 0.95c Time-dependent mass ejection. Time-dependent mass ejection. Multi-wavelength emission from both disk and jets. Multi-wavelength emission from both disk and jets. Synchrotron emission ~ magnetic field. Synchrotron emission ~ magnetic field. Quasi-Periodic Oscillations (QPO) in X-rays, etc … (see e.g. Tagger et al.) Quasi-Periodic Oscillations (QPO) in X-rays, etc … (see e.g. Tagger et al.) Few pc Mirabel et al(1998)

5. Seminaire MHD, ENS Paris, 25/09/06 5 Active galactic nuclei  AGN = radio-loud galaxies with twin jets Central objects: super-massive BH Central objects: super-massive BH V jet ~ 0.1c to  ~ 10 V jet ~ 0.1c to  ~ 10 Non-thermal emission ranging from radio to  -rays (synchrotron, SSC, IC) Non-thermal emission ranging from radio to  -rays (synchrotron, SSC, IC) 2 classes of AGN: FRI and FRII. 2 classes of AGN: FRI and FRII. FRII jets are likely to have two components(hadrons and/or pairs). FRII jets are likely to have two components(hadrons and/or pairs).  Jets and disk luminosities linked. Serjeant et al(1998) M87

6. Seminaire MHD, ENS Paris, 25/09/06 6 Observations vs. Theory I  In all kind of systems we have: V jet ~ (2GM * /R * ) 1/2 => Jet matter is likely coming from a region close to the central object and gravity is the most probable source of energy. V jet ~ (2GM * /R * ) 1/2 => Jet matter is likely coming from a region close to the central object and gravity is the most probable source of energy. Magnetic field + plasma => MHD approach has to be considered. Magnetic field + plasma => MHD approach has to be considered. Some jets have two components => Various mechanisms may be working at once. Some jets have two components => Various mechanisms may be working at once. Same ingredients: central objects + accretion disks… Same ingredients: central objects + accretion disks…  Axisymmetry seems to be a good approximation as well as symmetry with respect to the accretion disk mid-plane.  Ejection occurs during times ~ many inner disk or objects rotations:

7. Seminaire MHD, ENS Paris, 25/09/06 7 Observations vs. Theory II  Three classes of steady-state, axisymmetric models have been considered 1) Accretion disk driven jets => Velocity distribution is consistent with obs. and it can account for a large radial extension. 2) Central object driven winds => Hot internal outflow but limited radial extension. 3) Magnetospheric winds => Limited radial extension but temperature not very different from the one associated to a disk-driven outflow. ã Astrophysical jets are likely to be the result of a combination of at least two of them.

8. Seminaire MHD, ENS Paris, 25/09/06 8 Models outlines Disk-driven jet Magneto- spheric wind Central object YSO Kerr BH Energy source Gravity via disk angular momentum Magnetic reconnection or disk angular momentum Rotational energy of the object Origin of the ejected matter A fraction of the disk material Stellar corona material Ergospheric pair plasma => MHD ?? Collimation mechanism Toroidal magnetic field External disk- driven jet ? Toroidal magnetic field or external disk-driven jet Models Requirements

9. Disk-driven jets Disk structure & equilibrium Magneto-centrifugal acceleration Self-similar calculations 2.5D numerical simulations Model based upon the idea of Blandford & Payne (1982)

10. Seminaire MHD, ENS Paris, 25/09/06 10  Stationary accretion: => The disk has to be resistive !  For non-resistive disks, the accretion is stopped by the advection of poloidal magnetic field. => The disk is prone to MHD turbulence.  The magnetic torque brakes disk material: => Disk angular momentum removal provokes a magnetic twisting (B  Disk angular momentum removal provokes a magnetic twisting (B  <0)  Angular momentum is stored in the magnetic field and is transported along the poloidal magnetic field. Disk magnetic braking

11. Seminaire MHD, ENS Paris, 25/09/06 11 Disk Equilibrium  Disk vertical balance is made of 3 forces: 1. Gravity pinching the disk. 2. Magnetic pinching of the disk 3. Thermal pressure gradient lifting matter.  In order to lift a small fraction of the disk matter in the jet => P  o /B 2  1.  The magnetic field has to collimate the outflow so that P  o /B 2 cannot be >> 1 ( Ferreira & Pelletier 1995). Near-equipartition disk seems to be the most promising structure for stationary jet launching !

12. Seminaire MHD, ENS Paris, 25/09/06 12 Magneto-centrifugal acceleration I  Poloidal and toroidal magnetic forces are closely related:  In order to accelerate matter, the magnetic torque has to become positive! =>Increase of the centrifugal force  Both magnetic force & centrifugal force speed up matter in the poloidal plane. (JxB).B p (JxB).B 

13. Seminaire MHD, ENS Paris, 25/09/06 13 Magneto-centrifugal acceleration II  The centrifugal force has to overcome the gravitational attraction:  Opening angle of the field lines has to be larger than 30 o at the disk surface, in the case of a “cold” plasma.  The magnetic field may collimate the jet. Blandford & Payne (1982)

14. Seminaire MHD, ENS Paris, 25/09/06 14 Magneto-centrifugal Acceleration III  In a stationary ideal MHD framework => MHD invariants Frozen-in field Frozen-in field Angular momentum Angular momentum Specific energy (Bernoulli) Specific energy (Bernoulli)  Acceleration takes place if RB  decreases (MHD jet) and/or if C S decreases (thermal wind).  RB   MHD current => current circuit in accretion- ejection do have a “butterfly” shape..  Terminal velocity V 2 max = 2E(a) RB  =cst

15. Seminaire MHD, ENS Paris, 25/09/06 15 Self-similar Model  Accretion-ejection structures has to deal with both resistive and ideal MHD equations.  Simplification: writing all quantities as This is inspired from the shape of the driving force: gravity!  Description valid for large launching array..  We obtain a 1D problem to solve with 3 critical points. Slow and fast magnetosonic points Slow and fast magnetosonic points Alfvèn point. Alfvèn point.  Resistivity has to be prescribed as a spatially varying quantity, e.g. as a Shakura-Sunyaev prescription.

16. Seminaire MHD, ENS Paris, 25/09/06 16 Self-similar Calculations  Blandford & Payne (1982): 1st cold self-similar jets  Konigl(1989):1st simplified turbulent disks study  Wardle & Konigl (1993),Li(1995,1996):1st disk-jet connections but with huge simplifications in the context of ambipolar diffusion.  Ferreira & Pelletier(1995):1st complete disk-jet connections with prescribed Ohmic resistivity.  Ferreira(1997):1st trans-Alfvenic jets including complete disk structure (Ohmic resistivity).  Casse & Ferreira (2000): implementation of turbulent viscosity in the disk and coronal heating.  Vlahakis et al(2000):1st jet crossing all critical surfaces.  Ferreira & Casse (2004): 1st jet crossing all critical surfaces with complete disk structure.

17. Seminaire MHD, ENS Paris, 25/09/06 17 MHD Jet simulations  Jet simulations with various initial conditions Ustyugova et al. (1995,1998) Ustyugova et al. (1995,1998) Romanova et al. (1997) Romanova et al. (1997) Ouyed et Pudritz (1997,1999) Ouyed et Pudritz (1997,1999) Krasnopolsky et al. (1999,2003) Krasnopolsky et al. (1999,2003) Fendt & Cemeljic (2002) Fendt & Cemeljic (2002) Rekowski & Brandenburg (2004) Rekowski & Brandenburg (2004) Anderson el al. (2005), etc… Anderson el al. (2005), etc… Quasi-stationary jet solutions crossing all critical surfaces.  Accretion disk is treated as a boundary condition. Krasnopolsky et al(1999)

18. Seminaire MHD, ENS Paris, 25/09/06 18 Disk-Jet simulations  Some works have tried to described both disk and jet:  Ideal MHD Shibata & Ushida (1985) Shibata & Ushida (1985) Stone & Norman (1996) Stone & Norman (1996) Matsumoto et al. (1996) Matsumoto et al. (1996) Kudoh et al. (1998) Kudoh et al. (1998) Kato et al.(2002), etc.. Kato et al.(2002), etc..  Resistive MHD Kuwabara et al.(2005) Kuwabara et al.(2005)  Resistive disk & Ideal jet Casse & Keppens (2002,2004) => Casse & Keppens (2002,2004) =>  3D simulations have been performed but without reaching steady-state (e.g. Kigure & Shibata 2005).

19. Seminaire MHD, ENS Paris, 25/09/06 19Accretion-ejection Current circuit Poynting flux & Streamlines Casse & Keppens (2004)

20. YSO Winds and Disk-driven Jets Stellar winds X-wind Magnetospheric winds

21. Seminaire MHD, ENS Paris, 25/09/06 21 Stellar Winds  Since solar wind model (Parker 1958), stars are expected to produce outflows.  Stellar winds needs coronal heating at the base of the flow to overcome gravity..  No MHD Poynting flux near the rotation axis !!  MHD stellar outflows may become collimated if the central object is rotating fast enough (e.g. Bogovalov & Tsinganos (1999), Sauty et al. 2004, Matt & Balick 2004). Sauty et al. (2004)

22. Seminaire MHD, ENS Paris, 25/09/06 22 Stellar wind & rotation  Low-mass YSO are slow rotators:  No self-induced collimation !  Disk-driven jets do have a hollow structure.  Coronal heating may be provoked by matter falling onto the star and/or MHD turbulence.  Stellar wind collimation may be provided by the external disk-driven jet.  Protostars can be spun down by the stellar wind if R A >> R STAR and/or if the wind mass loss rate is large ! Matt & Pudritz (2005) Coronal Heating Hartmann & Stauffer (1989)

23. Seminaire MHD, ENS Paris, 25/09/06 23 Two-component YSO jets  Disk-driven jet simulations with inner stellar wind  Study of both collimation and stellar wind heating Meliani, Casse & Sauty (2006) Steady stellar mass ejection Mass ejected with  Mass ejected with V ej ~ 0.01 V Alfven  Magnetic field at star surface ~ 2kG  Resistivity in the stellar wind => Ohmic Heating !

24. Seminaire MHD, ENS Paris, 25/09/06 24 Two-component YSO jet  Collimation occurs whatever the stellar wind ejection rate (here 10 -9 solar mass/yr) !  Star braking may be efficient since R A /R * ~ few tens..  No conclusion since we do not have the inner radius of the disk ! Fast-magnetosonic surface Alfven surface Slow-magnetosonic surface Stellar wind hot component T~5.10 5 K Disk-driven cooler component T~ 6.10 4 K Thermal energy released in the wind ~ 35% of accretion energy !! M A =10 -7 M  /yr M Jet =10 -8 M  /yr M Jet/ M W =10

25. Seminaire MHD, ENS Paris, 25/09/06 25 YSO Jet collimation Stellar wind mass rate 10 -7 M  /yr  Stellar wind mass rate 10 -7 M  /yr  Larger disk-driven jet ejection rate increases as well as the jet radius  more efficient magneto-centrifugal acceleration !! Stellar wind pressur e Larger centrifugal force Enhanced accretion

26. Seminaire MHD, ENS Paris, 25/09/06 26 X-wind model  X-wind model (Shu et al. 1994,2000): similar to disk-driven jet except for disk magnetic flux (tiny here leads to R IN  R OUT ).  Magnetic field comes from stellar magnetopshere.  The wind is powered by accreting material !  X-wind cannot spin down protostars  A viscous torque has to provide accretion rate. Ejection rate / Accretion rate ~ 1/3 to fit observations. Ejection rate / Accretion rate ~ 1/3 to fit observations. Collimation is a crucial issue  Collimation is a crucial issue e.g. Pudritz et al. (2006).  Angular momentum budget does not fit observations (so as radial profiles).

27. Seminaire MHD, ENS Paris, 25/09/06 27 Magnetospheric ejection  Stellar braking may occur if its magnetosphere is anchored in the disk beyond corotation radius  Ejection arises from reconnection points Parallel Star dipole (ReX-winds): Disk material is lifted by the reconnecting field lines (e.g. Hirose et al. 1997,Ferreira et al. 2000)=> Unsteady ejection Parallel Star dipole (ReX-winds): Disk material is lifted by the reconnecting field lines (e.g. Hirose et al. 1997,Ferreira et al. 2000)=> Unsteady ejection Anti-parallel stellar dipole (e.g. Goodson et al.1997, Matt et al.2002) => “CME- like ejection of coronal matter => Unsteady ejection Anti-parallel stellar dipole (e.g. Goodson et al.1997, Matt et al.2002) => “CME- like ejection of coronal matter => Unsteady ejection  This kind of magnetospheric ejection can occur in the hollow part of a disk- driven jet => Presence of a hot, unsteady internal jet component. Ferreira et al.(2006) ReX-wind Anti-parallel dipole

28. Seminaire MHD, ENS Paris, 25/09/06 28 Concluding remarks I  YSO disk-driven jets Launching and collimation mechanisms are now quite understood. Launching and collimation mechanisms are now quite understood.  Disk-driven jet is likely to be the external envelope of Yso jets.. Some observational features can be reproduced by MHD simulations. Some observational features can be reproduced by MHD simulations.BUT Disk magnetic field origin is not yet completely clear: Disk magnetic field origin is not yet completely clear:  Dynamo generated and/or dynamically advected? Yso disk turbulence origin is still unclear as well as turbulence transport coefficients (e.g.equipartition disks): Yso disk turbulence origin is still unclear as well as turbulence transport coefficients (e.g.equipartition disks):  Relative amplitude of resistivity and/or turbulent viscosity, role of the ambipolar diffusion… Heating and cooling terms are not fully taken into account in the MHD energy equation : Heating and cooling terms are not fully taken into account in the MHD energy equation :  No direct comparison with observations.. 3D stability of disk-jet systems is not yet clearly addressed. 3D stability of disk-jet systems is not yet clearly addressed.

29. Seminaire MHD, ENS Paris, 25/09/06 29 Concluding remarks II  Yso stellar winds Stellar winds may carry away star angular momentum Stellar winds may carry away star angular momentum We have to understand how accretion energy may be massively converted into thermal energy in the stellar corona. We have to understand how accretion energy may be massively converted into thermal energy in the stellar corona. Stellar wind may account for inner yso jet hot component since embedding disk-driven jets seem to remain cylindrical. Stellar wind may account for inner yso jet hot component since embedding disk-driven jets seem to remain cylindrical.  Magnetospheric winds “Disk-locking” models spinning-down is inefficient for measured dipolar magnetic field B DIP < 200 G (Johns-Krulls et al. 1999). “Disk-locking” models spinning-down is inefficient for measured dipolar magnetic field B DIP < 200 G (Johns-Krulls et al. 1999). Magnetospheric mechanisms likely produce unsteady ejection. Magnetospheric mechanisms likely produce unsteady ejection.  They may contribute for time dependent spectral fluctuations  They may contribute for time dependent spectral fluctuations  X-wind models  X-winds cannot spin down the star…  X-winds cannot spin down the star…  X-wind cannot achieve cylindrical collimation (e.g. Pudritz et al.2006)  X-wind cannot achieve cylindrical collimation (e.g. Pudritz et al.2006)