Probing the role of dynamical friction in shaping the BSS radial distribution. I - Semi-analytical models and preliminary N-body simulations

TL;DR

This study uses semi-analytical models and N-body simulations to investigate how dynamical friction influences the radial distribution of Blue Straggler Stars in globular clusters, revealing the formation of bimodal distributions and a persistent central peak.

Contribution

It demonstrates that dynamical friction alone can produce bimodal BSS distributions and a stable central peak, aligning with observations, through semi-analytical and simplified N-body models.

Findings

Dynamical friction causes a bimodal BSS distribution with a moving dip.

A stable central peak forms in N-body simulations regardless of initial conditions.

Distribution evolves from bimodal to monotonic over time.

Abstract

We present semi-analytical models and simplified $N$-body simulations with $10^4$ and $10^5$ particles aimed at probing the role of dynamical friction (DF) in determining the radial distribution of Blue Straggler Stars (BSSs) in globular clusters. The semi-analytical models show that DF (which is the only evolutionary mechanism at work) is responsible for the formation of a bimodal distribution with a dip progressively moving toward the external regions of the cluster. However, these models fail to reproduce the formation of the long-lived central peak observed in all dynamically evolved clusters. The results of $N$-body simulations confirm the formation of a sharp central peak, which remains as a stable feature over the time regardless of the initial concentration of the system. In spite of a noisy behavior, a bimodal distribution forms in many cases, with the size of the dip increasing as a function of time. In the most advanced stages the distribution becomes monotonic. These results are in agreement with the observations. Also the shape of the peak and the location of the minimum (which in most of the cases is within 10 core radii) turn out to be consistent with observational results. For a more detailed and close comparison with observations, including a proper calibration of the timescales of the dynamical processes driving the evolution of the BSS spatial distribution, more realistic simulations will be necessary.