Explosive Ejections Generated by Gravitational Interactions

During the fragmentation and collapse of a molecular cloud, it is expected that it will have close encounters with (proto)stellar objects that can lead to the ejection of a fraction of them as runaway objects. However, the duration and consequences of such encounters are perhaps small enough for there to be no direct evidence of their occurrence. As a first approximation, herein we analytically study the interaction of a massive object that moves at high velocity into a cluster of negligible-mass particles with an initial number density distribution ∝ R ^−α. We have found that the runaway conditions of the distribution after the encounter are related to the mass and the velocity of the star and the impact parameter of each particle to the stellar object. Then, the cluster particles are gravitationally accelerated by the external approaching star, destroying the cluster, and the dispersion and velocities of the particles have explosive characteristics. We compare this analytical model with several numerical simulations and, finally, apply our results to the Orion fingers in the Orion BN/KL region, which show an explosive outflow that could be triggered by the gravitational interaction of several (proto)stellar objects.