The Origin of OB Runaway Stars

TL;DR

This paper proposes that OB runaway stars originate from gravitational interactions in young star clusters, explaining their high velocities and mass distribution, supported by simulations matching observed properties.

Contribution

It introduces a model where OB runaways are ejected through interactions in collapsing young star clusters, providing a natural explanation for their velocities and mass distribution.

Findings

Model replicates observed velocities and mass distribution of OB runaways.

Explains high-velocity stars around young clusters like R136 and Westerlund 2.

Supports the idea that most massive stars form in dense, low-mass clusters.

Abstract

About 20% of all massive stars in the Milky Way have unusually high velocities, the origin of which has puzzled astronomers for half a century. We argue that these velocities originate from strong gravitational interactions between single stars and binaries in the centers of star clusters. The ejecting binary forms naturally during the collapse of a young ($\aplt 1$\,Myr) star cluster. This model replicates the key characteristics of OB runaways in our galaxy and it explains the $\apgt 100$\,\Msun\, runaway stars around young star clusters, e.g. R136 and Westerlund~2. The high proportion and the distributions in mass and velocity of runaways in the Milky Way is reproduced if the majority of massive stars are born in dense and relatively low-mass (5000-10000 \Msun) clusters.