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MHD Simulations of Flares and Jets in the Sun, Stars, and Accretion Disks

East Asia Numerical Astrophysics Meeting Oct. 31, 2006 Taejeon, Korea 25min talk + 5min discussion. MHD Simulations of Flares and Jets in the Sun, Stars, and Accretion Disks. Kazunari Shibata Kwasan and Hida Observatories Kyoto University. Contents.

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MHD Simulations of Flares and Jets in the Sun, Stars, and Accretion Disks

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  1. East Asia Numerical Astrophysics Meeting Oct. 31, 2006 Taejeon, Korea 25min talk + 5min discussion MHD Simulations of Flares and Jets in the Sun, Stars, and Accretion Disks Kazunari Shibata Kwasan and Hida Observatories Kyoto University

  2. Contents • Introduction • Solar Flares and Jets • （Protostellar Flares and Jets) • Jets from Accretion Disks - With emphasis on magnetic reconnection

  3. universe is full of flares Protostellar flares Solar flares Gamma ray bursts

  4. universe is full of jets and mass ejections protostellar jets Coronal mass ejections Solar jets AGN (active galactic nuclei) jets

  5. Basic MHD processes in stars and disks

  6. Solar Flares

  7. various “flares” with different appearance microflares with jets impulsive flares Giant arcade Long duration flares

  8. Plasmoid (flux rope) ejectionsare ubiquitous in flares Unified model coronal mass ejections above giant arcades ~ 1011 cm Long Duration flares ~ 1010 cm impulsive flares ~ 109 cm Plasmoid-Induced-Reconnection (Shibata 1999)

  9. Unified model(plasmoid-induced reconnection model: Shibata 1999) (a,b)： giant arcade, long duration/ impulsive flare (c,d) ：impulsive flares, microflares Energy release rate＝

  10. Soft X-ray intensity of solar corona during a week (all bursts are flares) What determines flare duration ? Nishida et al. (2006a) In preparation

  11. What determines flare duration ? Flare duration ~ reconnection time After Plasmoid ejection L Field lines whch can be reconnected Initial condition Potential field (minimum energy state)

  12. Various cases with different size and field strength of reconnection region I Shiota et al. (2005) II Large Weak III IV Small strong

  13. Case of large reconnection region • Color: gas pressure • Contour: field lines • Long duration

  14. Case of small reconnection region • Color: gas pressure • Contour: field lines • Short duration

  15. Reconnected flux as a function of time Reconnected flux per unit time • Duration become shorter when the reconnection size is small (and magnetic field strength is stronger) t/tA

  16. Normalized reconnection rate Normalized Reconnection rate • Duration become shorter when the reconnection region is smaller t/tA

  17. Comparison with observations(Nagashima and Yokoyama 2006) • Simulation data are plotted on Nagashima & Yokoyama (2006)’s figure • Flare duration is different even when the flare loop lengths are similar Flare loop length

  18. Soft X-ray intensity of solar corona during a week (all bursts are flares) What determines reconnection rate(energy release rate) ? Nishida et al. (2006b) In preparation

  19. Role of Plasmoidplasmoid-induced-reconnection(Shibata et al. 1995, 1999,Shibata and Tanuma 2001)

  20. Model of impulsive flares Nishida et al. 2006b in preparation

  21. Two cases • Case 1 : resistivity is changed • Case 2:plasmoid velocity is changed (due to external force)

  22. Case 1: resistivity is changed Plasmoid velocity Rise velocity of Loop (Reconnection rate)

  23. Case 2: plasmoid velocity is changed by external force Reconnection rate Plasmoid velocity

  24. ⊿ｈ □： ～20” ○: 10-15” △: 5-10” ×: < 5” ○ ○ △ Veje (km/s) △ (□) × (×) Vloop (km/s) Observed correlation between Vloop and Veje(Shimizu et al. 2006 in preparation)

  25. Plasmoid-induced reconnectionin a fractual current sheet(Tanuma et al. 2001, Shibata and Tanuma 2001) plasmoid Reconnection rate Vin/VA time Tanuma et al. (2001)

  26. Simulations of smaller flares - reconnection driven by emerging flux (Parker instability) Shimizu et al. (2006) In preparation Isobe et al., (2005) Nature Isobe et al. (2006) PASJ

  27. Reconnection driven by emerging flux Model of solar jet (Shimizu et al. 2006, in preparation) Same as Yokoyama and Shibata (1995) But with CIP scheme (200x110) Solar jet

  28. Reconnection driven by emerging flux :case of vertical field (Shimizu et al. 2006) This model is useful as model of generation of Alfven waves,which accelerate high speed Solar wind (Parker 1991, Axford and McKenzie 1996, cf) Kudoh and Shibata 1999, Suzuki and Inutsuka 2005)

  29. z y x 3D-MHD modeling of emerging flux using the Earth simulator (Isobe et al., 2005,Nature 434, 476) t=50 t=70 t=90 800x400x600 blue：iso-magnetic field strength surface、 side ：temperature

  30. Comparison with observed H alpha arch filament(Isobe et al. Nature 2005) Hα（Hida） Density isosurface density~1012/cc, temperature~10000K Length~10000km, width~1000km

  31. z y x 3D structure as a result of Rayleigh-Taylor instability (Isobe et al. Nature 2005, Isobe et al. PASJ 2006) Density • Top of emerging flux becomes top-heavy, so that Rayleigh-Taylor instability occurs. • As a result, filamentary structures along magnetic field lines are created • mushroom type vortex motions (due to KH instability) are seen • 3D patchy reconnection occurs

  32. Filamentary jet produced by 3D patchy reconnection(Isobe et al. 2005 Nature) Halpha HIda EUV TRACE simulation observations

  33. Reported in Newspapers …

  34. Jets and flares in accretion disks

  35. 3D structure of jets from disks(Kigure and Shibata 2005) Non-axisymmetric structure appeared in a disk And propagate into jets Model R6

  36. Very weak field case:Magnetic buoyancy driven outflow(Kigure and Shibata 2006 in prep) Magnetic buoyancy is a main force of acceleration !

  37. Do jets and disks reach steady state ? No !!, because Magnetorotational Instability is so powerful (Balbus and Hawley 1991) Disks are full of reconnection events Kudoh et al 2002 Sato et al. 2005 Ibrahim et al. 2005

  38. Long term simulations of jets from accretion disks(Ibrahim and Shibata 2006, see poster) Region size in previous simulations (Kudoh et al. 1998, 2002, KatoS et al. 2004)

  39. Quasi-periodic ejections of jets(see Ibrahim’s poster) Period is roughly determined by Alfven time

  40. General relativistic jets from Kerr hole(Koide et al. 2006 Phys Rev, listen to his talk)

  41. Summary • Reconnection model of solar flares has been developed significantly in these 10 years owing to rapid progress of space observations and supercomputer, though key puzzles remained: triggering mechanism, coronal heating, micro-macro coupling. • MHD simulations of astrophysical jets have also been developed significantly, including general relativistic model. Remaning important questions are: collimation, 3D stability of jets, and production of ultra relativistic jets (Lorentz factor > 10). • jets and disksnever reach steady state, and are full of reconnection events I hope more and more astrophysicists will join this exciting field “astrophysical reconnection” !

  42. Protostellar flares and jets Uehara et al. (2006) in preparation Kawamiti and Shibata (2006) in preparation

  43. reconnection modelof protostellar flareand jets（Hayashi, Shibata, Matsumoto 1996)

  44. Many reconnection events (flares)(Uehara et al. 2006 in preparation) Emg = 2x10^{-5}

  45. Global and long term simulations(Uehara et al 2006 in prep)

  46. Global simulation(Uehara et al. 2006 in preparation) Protostellar jets

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