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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 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
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
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
Starburst Rings NGC4313 NGC1512 NGC6782
NGC 1068 • Type : Sb / AGN • Distance : 14.4 Mpc ( H0 =75 km s-1 Mpc-1 ) 1 arcsec = 74 pc 9.5 arcmin
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
The Mechanism of Rayleigh’s Criterion for Shear Instability (C.C. Lin 1944)
Vorticity Creation by Shock(Cocco, Truesdell, Lighthill, Hayes, Berndt, Kevlahan)
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.