Decline of the current quadrupole moment during the merger phase of   binary black hole coalescence
  Utilizing the tools of tendex and vortex, we study the highly dynamic plunge and merger phases of several $\pi$-symmetric binary black hole coalescences. In particular, we observe a decline of the strength of the current quadrupole moment as compared to that of the mass quadrupole moment during the merger phase, contrary to a naive estimate according to the dependence of these moments on the separation between the black holes. We further show that this decline of the current quadrupole moment is achieved through the remnants of the two individual spins becoming nearly aligned or anti-aligned with the total angular momentum. We also speculate on the implication of our observations for achieving a consistency between the electric and magnetic parity quasinormal modes. 
Fan Zhang
gr-qc