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4.7. Bar destruction

The inflow of matter in the center can destroy the bar. It is sufficient that 5% of the mass of the disk has sunk inside the inner Lindblad resonance (Hasan & Norman 1990, Pfenniger & Norman 1990, Hasan et al 1993). But this depends on the mass distribution, on the size of the central concentration; a point mass like a black hole is more efficient (may be 2% is sufficient). The destruction is due to the mass re-organisation, that perturbs all the orbital structure: the x1 orbits sustaining the bar for instance are shifted outwards. Near the center, the central mass axisymmetrizes the potential. Then there is a chaotic region, and outside a regular one again. When a central mass concentration exists initially, in N-body simulations, a bar still forms, but dissolves more quickly. It is also possible that after a bar has dissolved, another one forms, after sufficient gas accretion to generate new gravitational instabilities: the location of the resonances will not be the same.