Time evolution of the galaxy and the SMBH binary parameters. Top left: volume–density profiles of the NGC 4486B model at different times during the SMBH binary evolution. Top right: orbit of the SMBH binary in the reference frame of the stellar density center. The time-colored line shows the trajectory of the binary CoM after subtracting the density center motion; the density center itself is shown at the origin with a red dot. Bottom left: velocity of the SMBH binary CoM relative to the density center, illustrating the residual motion of the binary within the host galaxy. Bottom right: velocities of the individual SMBHs relative to the binary CoM, showing that the lighter secondary SMBH moves faster than the primary and that both velocities increase as the binary hardens.