The final-parsec problem in non-spherical galaxies revisited

Understand

We consider the evolution of supermassive black hole binaries at the center of spherical, axisymmetric, and triaxial galaxies, using direct N-body integrations as well as analytic estimates.

• We find that the rates of binary hardening exhibit a significant N-dependence in all the models, at least for N in the investigated range of 10^5<=N<=10^6.
• Binary hardening rates are also substantially lower than would be expected if the binary loss cone remained full, as it would be if the orbits supplying stars to the binary were being efficiently replenished.
• The difference in binary hardening rates between the spherical and nonspherical models is less than a factor of two even in the simulations with the largest N.