Globular Cluster Mass Loss in the Context of Multiple Populations

TL;DR

This paper challenges the idea that globular clusters were significantly more massive at birth to explain multiple populations, suggesting instead that their initial star composition was already enriched, which questions existing self-enrichment models.

Contribution

It proposes that globular clusters did not undergo substantial mass loss and that their current enriched star fractions reflect initial conditions, contradicting previous mass loss-based theories.

Findings

Uniform enriched fraction across 33 GCs suggests minimal mass loss.

Mass loss models predict correlations not observed in data.

Initial star composition likely accounts for multiple populations.

Abstract

Many scenarios for the origin of the chemical anomalies observed in globular clusters (GCs; i.e., multiple populations) require that GCs were much more massive at birth, up to $10-100\times$, than they are presently. This is invoked in order to have enough material processed through first generation stars in order to form the observed numbers of enriched stars (inferred to be second generation stars in these models). If such mass loss was due to tidal stripping, gas expulsion, or tidal interaction with the birth environment, there should be clear correlations between the fraction of enriched stars and other cluster properties, whereas the observations show a remarkably uniform enriched fraction of $0.68\pm0.07$ (from 33 observed GCs). If interpreted in the heavy mass loss paradigm, this means that all GCs lost the same fraction of their initial mass (between $95-98$\%), regardless of their mass, metallicity, location at birth or subsequent migration, or epoch of formation. This is incompatible with predictions, hence we suggest that GCs were not significantly more massive at birth, and that the fraction of enriched to primordial stars observed in clusters today likely reflects their initial value. If true, this would rule out self-enrichment through nucleosynthesis as a viable solution to the multiple population phenomenon.