We study the effect of a massive central singularity on the structure of a triaxial galaxy using N-body simulations. Starting from a single initial model, we grow black holes with various final masses Mh and at various rates, ranging from impulsive to adiabatic. In all cases, the galaxy achieves a final shape that is nearly spherical at the center and close to axisymmetric throughout. However, the rate of change of the galaxy's shape depends strongly on the ratio Mh/Mg of black hole mass to galaxy mass. When Mh/Mg 0.3%, the galaxy evolves in shape on a timescale that exceeds 102 orbital periods, or roughly a galaxy lifetime. When Mh/Mg 2.5%, the galaxy becomes axisymmetric in little more than a crossing time. We propose that the rapid evolution toward axisymmetric shapes that occurs when Mh/Mg 2.5% provides a negative-feedback mechanism that limits the mass of central black holes by cutting off their supply of fuel.
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