On The Run: How Fast Runaway Stars Can Escape From Their Home Cluster?

Sammanfattning: Galaxies contain a wide variety of star clusters with different properties. Each cluster is a possible source of runaway stars, which can be progenitors of supernovae in other parts of the galaxy than their home cluster. Considering runaway stars in galaxy simulations has shown to increase the galactic feedback. This project investigates how the initial condition of a star cluster affects the velocity distribution of runaway stars. To do this, I performed simulations of star clusters solving the N-body problem with the NBODY6tt code. First, different initial conditions for each cluster are simulated, with varying half mass radius and primordial binary fraction. This is followed by an analysis of the velocity distribution for each simulated cluster after 40 Myr. Dark matter is not taken into consideration in these simulation. Including dark matter components would imply an added gravitational force acting on each star in the cluster, and thus a higher escape velocity needed to be ejected. Thus, one can argue that including dark matter would result in less runaway stars being produced by the cluster, but should however be investigated further. With initial radii of 1 and 10 pc, the bigger clusters produce fewer runaway stars after 40 Myr compared to the cluster with a radius of 0.1 pc. This result is because the interaction rate between stars is longer for clusters with greater radii. The number of ejected stars from a system increases when primordial binaries are introduced. However, the velocity distribution of a bigger cluster does not change when increasing the binary fraction with a factor of 2. The results imply that initial conditions of the star cluster affect the velocities of runaway stars. Consequently, it means that if runaway stars are included in galaxy simulations, the variations of initial conditions in star clusters should be considered. Instead of generalising the velocity distribution of runaway stars, the differences shown in this project should be taken into account. It can change how far runaway stars travel away from their home cluster, but also how many of these stars end up in a new environment, far from their home cluster. Further investigation on which initial conditions affect the velocity distribution of runaway stars is needed. Especially a deeper understanding of how primordial binaries can be implemented in N-body simulations is of high interest. However, I leave it to future projects to continue an exploration of this parameter space in detail.