A dependence of binary and planetary system destruction on subtle variations in the substructure in young star-forming regions

TL;DR

This study uses simulations to show how subtle variations in the initial substructure of star-forming regions influence the destruction rates of planetary systems and stellar binaries, with effects depending on binary separation and environment kinematics.

Contribution

It extends previous work by analyzing the impact of substructure on binary populations, revealing how environment and binary separation influence destruction likelihood.

Findings

More substructured regions disrupt more close binaries.

Wider binaries are more disrupted in smooth regions.

Differences in binary destruction are small and likely unobservable.

Abstract

Simulations of the effects of stellar fly-bys on planetary systems in star-forming regions show a strong dependence on subtle variations in the initial spatial and kinematic substructure of the regions. For similar stellar densities, the more substructured star-forming regions disrupt up to a factor of two more planetary systems. We extend this work to look at the effects of substructure on stellar binary populations. We present $N$-body simulations of substructured, and non-substructured (smooth) star-forming regions in which we place different populations of stellar binaries. We find that for binary populations that are dominated by close ($<$100au) systems, a higher proportion are destroyed in substructured regions. However, for wider systems ($>$100au), a higher proportion are destroyed in smooth regions. The difference is likely due to the hard-soft, or fast-slow boundary for binary destruction. Hard (fast/close) binaries are more likely to be destroyed in environments with a small velocity dispersion (kinematically substructured regions), whereas soft (slow/wide) binaries are more likely to be destroyed in environments with higher velocity dispersions (non-kinematically substructured regions). Due to the vast range of stellar binary semimajor axes in star-forming regions ($10^{-2} - 10^4$au) these differences are small and hence unlikely to be observable. However, planetary systems have a much smaller initial semimajor axis range (likely $\sim$1 -- 100au for gas giants) and here the difference in the fraction of companions due to substructure could be observed if the star-forming regions that disrupt planetary systems formed with similar stellar densities.