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The instability of a self-gravitating gaseous disk

The instability of a self-gravitating gaseous disk. by Chi Yuan Institute of Astronomy & Astrophysics Academia Sinica, Taipei 11-01-2006. Collaborators: David C.C. Yen, L.H. Lin, H.H. Wang, C.C. Yang. Two kinds of instability in astrophysical disks.

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The instability of a self-gravitating gaseous disk

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  1. The instability of aself-gravitating gaseous disk by Chi Yuan Institute of Astronomy & Astrophysics Academia Sinica, Taipei 11-01-2006 Collaborators: David C.C. Yen, L.H. Lin, H.H. Wang, C.C. Yang

  2. Two kinds of instabilityin astrophysical disks • Toomre’s instability: starburst rings, star formation • Shear instability of Rayleigh’s type: associated with shocks, causing substructure, chaos and turbulence

  3. Governing Equations

  4. The Antares Code 大火程序 • Second-order 2-D Godunov codes • Based on exact Riemann solver • Coupled with the fft Poisson solver (non-periodic BC) for disk self-gravity • True radiation (non-reflecting) boundary conditions. • Cartesian and polar coordinates • Isothermal and polytropic gas • All codes parallelized

  5. Starburst Rings NGC4313 NGC1512 NGC6782

  6. Circumnuclear Disk in ngc1068

  7. Center of M51

  8. NGC 1068 • Type : Sb / AGN • Distance : 14.4 Mpc ( H0 =75 km s-1 Mpc-1 ) 1 arcsec = 74 pc 9.5 arcmin

  9. Nearly Flat Rotation Curve

  10. Cases of Double Resonances: OLR-OILR

  11. Toomre’s Instability

  12. Onset of Instability

  13. Disk Instability

  14. Sub-structure, feathers, chaos

  15. Sub-structure of M81

  16. M81

  17. Shear Instability

  18. Sub-structure, Patches, Chaos

  19. Rayleigh’s Shear Instability:(vorticity in the axisymmetric flow flield has a local extremum)vorticity divided by surface density orSpecific vorticity has a local extremum

  20. Specific Vorticity

  21. The Mechanism of Rayleigh’s Criterion for Shear Instability (C.C. Lin 1944)

  22. Simple Explanation of Rayleigh’s shear instability

  23. Specific Vorticity distribution

  24. Vorticity Creation by Shock(Cocco, Truesdell, Lighthill, Hayes, Berndt, Kevlahan)

  25. Creation of Vorticity along Shocks

  26. Conclusions • Disk instability is extremely important in astrophysics. • Toomre’s instability at work, giving rise starburst and star formation activities. It also explains the origin of the dense circumnuclear molecular disks observed in the center of many nearby galaxies. • Shear instability creates substructures, patches and chaos in the middle of the galactic disk where shocks are present. • We believe that the origin of the shear instability lies on the vorticity creation on shocks.

  27. Evolution of Streamlines

  28. Specific Vorticity at different resolution

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