MOCCA code for star cluster simulations - VI. Bimodal spatial distribution of blue stragglers

TL;DR

This study uses numerical simulations to analyze the formation and transient nature of bimodal spatial distributions of blue stragglers in globular clusters, challenging existing dynamical clock methods.

Contribution

It demonstrates the transient nature of bimodal distributions and questions the reliability of the radius of avoidance as a dynamical age indicator.

Findings

Bimodal distribution is a very transient feature.

The radius of avoidance can become out of sync with the distribution minimum.

The bimodal distribution can form and vanish within short timescales.

Abstract

The paper presents an analysis of formation mechanism and properties of spatial distributions of blue stragglers in evolving globular clusters, based on numerical simulations done with the MOCCA code. First, there are presented N-body and MOCCA simulations which try to reproduce the simulations presented by Ferraro (2012). Then, the agreement between N-body and the MOCCA code is shown. Finally, we discuss the formation process of the bimodal distribution. We report that so-called bimodal spatial distribution of blue stragglers is a very transient feature. It is formed for one snapshot in time and it can easily vanish in the next one. Moreover, we show that the radius of avoidance proposed by Ferraro (2012) goes out of sync with the apparent minimum of the bimodal distribution after about two half-mass relaxation times. This finding creates a real challenge for the dynamical clock, which uses this radius to determine the dynamical age of globular clusters. Additionally, the paper discusses a few important problems concerning the apparent visibilities of the bimodal distributions which have to be taken into account while studying the spatial distributions of blue stragglers.