On the Formation of Runaway Stars BN and x in the Orion Nebula Cluster
  We explore scenarios for the dynamical ejection of stars BN and x from source
I in the Kleinmann-Low nebula of the Orion Nebula Cluster (ONC), which is
important for being the closest region of massive star formation. This ejection
would cause source I to become a close binary or a merger product of two stars.
We thus consider binary-binary encounters as the mechanism to produce this
event. By running a large suite of $N$-body simulations, we find that it is
nearly impossible to match the observations when using the commonly adopted
masses for the participants, especially a source I mass of $7\:{\rm{M}}_\odot$.
The only way to recreate the event is if source I is more massive, i.e.,
$\sim20\:{\rm{M}}_\odot$. However, even in this case, the likelihood of
reproducing the observed system is low. We discuss the implications of these
results for understanding this important star-forming region.
