Monte Carlo simulations of multiple populations in globular clusters: constraints on the cooling flow vs. accretion scenario using million bodies simulations

TL;DR

This study uses large-scale Monte Carlo simulations to compare two main scenarios for the origin of multiple populations in globular clusters, finding that the cooling flow scenario better reproduces observed properties than the accretion scenario.

Contribution

It provides a detailed simulation-based comparison of the cooling flow and accretion models for multiple populations in globular clusters, highlighting the conditions under which each scenario aligns with observations.

Findings

Accretion onto proto-stellar disks cannot produce discrete populations unless disks last longer than 20 Myr.

Cooling flow scenario can reproduce observed population ratios with specific initial conditions.

Radial segregation predictions depend on the orbital parameters and potential model.

Abstract

I simulate the evolution of a stellar system hosting two stellar populations whose initial set up is defined according to the two main scenarios proposed for the origin of multiple populations in Galactic globular clusters: (i) formation of a second generation from a cooling flow of pristine+polluted gas and (ii) accretion of polluted gas onto the proto-stellar disks of a fraction of low-mass stars. For this purpose, Monte Carlo simulations containing from $10^{5}$ up to $3\cdot 10^{6}$ particles have been run including the effect of stellar evolution, binary interactions, external tidal field and a detailed modelling of the proto-stellar disk structure. The early accretion of gas onto proto-stellar disks is unable to produce discrete populations and to alter the chemical composition of a significant ($>10\%$) fraction of stars unless a disk lifetime larger ($t_{disk}\sim20~Myr$) than that predicted by models is assumed. Moreover, in this scenario the mixing timescale of the two populations is too short to reproduce the observed segregation of the chemically enriched population. On the other hand, simulations run within the cooling flow scenario can evolve after a Hubble time into stellar systems with a first-to-second population mass ratio similar to that observed in globular clusters, provided that an initial filling-factor $r_{h}/r_{J}>0.15$ is adopted. However, in the weak tidal field regime a radial segregation of the second population stronger than what observed in Milky Way globular clusters at large Galactocentric distances is predicted. This discrepancy disappears in simulations following eccentric orbits in a realistic axisymmetric potential.