Gravitational Slingshot of Young Massive Stars in Orion

The Orion Nebula Cluster (ONC) is the nearest region of massive star formation and thus a crucial testing ground for theoretical models. Of particular interest among the ONC's ∼1000 members are: θ 1 Ori C, the most massive binary in the cluster with stars of masses 38 and 9 M ☉ ; the Becklin-Neugebauer (BN) object, a 30 km s −1 runaway star of ∼8 M ☉ ; and the Kleinmann-Low (KL) nebula protostar, a highly obscured, ∼15 M ☉ object still accreting gas while also driving a powerful, apparently "explosive" outflow. The unusual behavior of BN and KL is much debated: How did BN acquire its high velocity? How is this related to massive star formation in the KL nebula? Here, we report the results of a systematic survey using ∼10 7 numerical experiments of gravitational interactions of the θ 1 C and BN stars. We show that dynamical ejection of BN from this triple system at its observed velocity leaves behind a binary with total energy and eccentricity matching those observed for θ 1 C. Five other observed properties of θ 1 C are also consistent with it having ejected BN and altogether we estimate that there is only a ≲ 10 −5 probability that θ 1 C has these properties by chance. We conclude that BN was dynamically ejected from the θ 1 C system about 4500 years ago. BN then plowed through the KL massive star-forming core within the last 1000 years causing its recently enhanced accretion and outflow activity.