On the Formation of Runaway Stars BN and x in the Orion Nebula Cluster

TL;DR

This study uses N-body simulations to investigate the dynamical ejection of stars BN and x from the Orion Nebula Cluster, finding that a more massive source I (~20 solar masses) is needed to reproduce observations, but the probability remains low.

Contribution

It provides the first detailed N-body simulation analysis of the BN and x ejection scenario, challenging previous assumptions about source I's mass.

Findings

Higher source I mass (~20 M_sun) is required to match observations.

Standard mass assumptions (~7 M_sun) cannot reproduce the ejection event.

Likelihood of reproducing the observed system is low even with increased mass.

Abstract

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.