Formation of new stellar populations from gas accreted by massive young star clusters

TL;DR

This study presents evidence that massive star clusters can accrete gas from their host galaxy discs, leading to multiple star formation episodes and explaining the multiple stellar populations observed in ancient globular clusters.

Contribution

It demonstrates that gas accretion from host galaxy discs can trigger secondary star formation in massive star clusters, providing a new explanation for multiple stellar populations.

Findings

Massive star clusters in the Magellanic Clouds show recent burst-like star formation.

Clusters could accrete enough gas from galactic discs to form new stars.

This process may explain the multiple stellar populations in globular clusters.

Abstract

Stars in star clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old globular clusters -- with ages greater than 10 billion years and masses of several hundred thousand solar masses -- often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often invoked as second-generation star-formation trigger. The initial cluster masses should be at least 10 times more massive than they are today for this to work. However, large populations of clusters with masses greater than a few million solar masses are not found in the local Universe. Here we report on three 1-2 billion-year-old, massive star clusters in the Magellanic Clouds, which show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could accrete sufficient gas reservoirs to form new stars if the clusters orbited in their host galaxies' gaseous discs throughout the period between their initial formation and the more recent bursts of star formation. This may eventually give rise to the ubiquitous multiple stellar populations in globular clusters.