Open Cluster Dynamics under the Influence of Outflow–Ambient Interactions

Stars with outflows impinging on ambient gas experience accelerations due to the gravitational feedback from the interaction morphology between the outflow and the ambient gas. Such “negative dynamical friction” (NDF), in contrast to the conventional “dynamical friction” (DF), is studied for its impact on the dynamics of open clusters (OCs) immersed in a uniform ambient gas. We modify the N -body integration code REBOUND with both NDF and DF implemented according to the outflow conditions of each star in a consistently constructed OC. The evolution of stars is also involved in determining the gas–star interactions throughout their stellar lives. Compared to DF-only and gas-free models with identical initial conditions, the NDF-affected cluster is puffier and evaporates faster, as indicated by various diagnostics, including lower velocity dispersions and larger half-mass and half-light radii. Neutron stars with fast winds are expelled from the cluster due to their intensive NDF effect, even without the “kicks” by asymmetric supernovae. Exploration of parameter space confirms that the NDF effect is generally enhanced with higher ambient gas densities, in qualitative agreement with the expression of acceleration. Outflow–ambient interactions should be considered for the proper interpretation of the stellar dynamics evolution in clusters.