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MHD Simulations of Flares and Jets in the Sun, Stars, and Accretion Disks Kazunari Shibata Kwasan and Hida Observatories Kyoto University East Asia Numerical.

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Presentation on theme: "MHD Simulations of Flares and Jets in the Sun, Stars, and Accretion Disks Kazunari Shibata Kwasan and Hida Observatories Kyoto University East Asia Numerical."— Presentation transcript:

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

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 Solar flares Protostellar flares Gamma ray bursts

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

5 Basic MHD processes in stars and disks

6 Solar Flares

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

8 coronal mass ejections above giant arcades ~ cm Plasmoid (flux rope) ejections are ubiquitous in flares impulsive flares ~ 10 9 cm Long Duration flares ~ cm Unified model 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 What determines flare duration ? Nishida et al. (2006a) In preparation Soft X-ray intensity of solar corona during a week (all bursts are flares)

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

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

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 Duration become shorter when the reconnection size is small (and magnetic field strength is stronger) t/t A Reconnected flux per unit time

16 Normalized reconnection rate Duration become shorter when the reconnection region is smaller t/t A Normalized Reconnection rate

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

19 Role of Plasmoid plasmoid- 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 V loop (km/s) V eje (km/s) × (×) △ △ ○ (□) ○ □ : ~ 20” ○: 10-15” △ : 5-10” ×: < 5” ⊿h⊿h Observed correlation between V loop and V eje (Shimizu et al in preparation)

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

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

28 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) Reconnection driven by emerging flux : case of vertical field (S himizu et al. 2006)

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

30 Comparison with observed H alpha arch filament (Isobe et al. Nature 2005) Hα ( Hida ) Density isosurface density~10 12 /cc, temperature~10000K Length~10000km, width~1000km

31 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 x z y

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

33 Reported in Newspapers …

34 Jets and flares in accretion disks

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

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 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 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 disks never reach steady state, and are full of reconnection events I hope more and more astrophysicists will join this exciting field “astrophysical reconnection” !

42

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

44 reconnection model of protostellar flare and jets ( Hayashi, Shibata, Matsumoto 1996)

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

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

47 Global simulation (Uehara et al in preparation) Protostellar jets


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