**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 *x*_{1} 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.