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Two-Stream Instability of Counter-Rotating Galaxies | | R.V.E. Lovelace
; K.P. Jore
; M.P. Haynes
; | | Date: |
14 May 1996 | | Abstract: | The present study of the two-stream instability in stellar disks with counter-rotating components of stars and/or gas is stimulated by recently discovered counter-rotating spiral and S0 galaxies. Strong linear two-stream instability of tightly-wrapped spiral waves is found for one and two-armed waves with the pattern angular speed of the unstable waves always intermediate between the angular speed of the co-rotating matter ($+Omega$) and that of the counter-rotating matter ($-Omega$). The instability arises from the interaction of positive and negative energy modes in the co- and counter-rotating components. The unstable waves are in general convective - they move in radius and radial wavenumber space - with the result that amplification of the advected wave is more important than the local growth rate. For a galaxy of co-rotating stars and counter-rotating stars of mass-fraction $xi_* < {1over 2}$, or of counter-rotating gas of mass-fraction $xi_g < {1over 2}$, the largest amplification is usually for the one-armed leading waves (with respect to the co-rotating stars). For the case of both counter-rotating stars and gas, the largest amplifications are for $xi_*+xi_g approx {1over 2}$, also for one-armed leading waves. The two-armed trailing waves usually have smaller amplifications. The growth rates and amplifications all decrease as the velocity spreads of the stars and/or gas increase. It is suggested that the spiral waves can provide an effective viscosity for the gas causing its accretion. | | Source: | arXiv, astro-ph/9605076 | | Services: | Forum | Review | PDF | Favorites | |
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