2007MNRAS.377..459S

Interactions between pairs of binary stars play an important role in the dynamics of dense stellar systems. One possible outcome of a binary-binary encounter is full ionization: the destruction of both interacting binaries resulting in four separating single stars. This process is only possible for positive total energy, and the cross-section for full ionization falls to zero at zero total energy. In the context of a stellar system, full ionization is most likely to involve the interaction of two soft binaries with low binding energies. We consider the case where the four stars have a similar mass and derive an asymptotic power law relating the cross-section for full ionization with the total energy when this latter quantity is small. Our new theory makes use of the fact that the most dramatic changes in scale and energies of a few-body system occur when its components pass near to a central configuration. Numerical simulations are used to verify the result.