Superbubble dynamics in globular cluster infancy II. Consequences for secondary star formation in the context of self-enrichment via fast rotating massive stars

TL;DR

This paper investigates how supernovae and dark remnant accretion influence gas retention and second star formation in globular clusters, focusing on the role of fast rotating massive stars in self-enrichment during early cluster evolution.

Contribution

It provides a detailed timeline of globular cluster evolution, highlighting the phases of wind bubble, supernova, and dark remnant accretion, and explores the conditions for second generation star formation.

Findings

Gas is compressed into filaments by stellar winds, inhibiting star formation during the wind bubble phase.

Second generation stars can form in accretion discs fed by FRMS ejecta and pristine gas.

Dark remnant accretion may lead to rapid gas expulsion, affecting cluster evolution.

Abstract

The self-enrichment scenario for globular clusters (GC) requires large amounts of residual gas after the initial formation of the first stellar generation. Recently, Krause et al. (2012) found that supernovae may not be able to expel that gas, as required to explain their present day gas-free state, and suggested that a sudden accretion on to the dark remnants, at a stage when type II supernovae have ceased, may plausibly lead to fast gas expulsion. Here, we explore the consequences of these results for the self-enrichment scenario via fast rotating massive stars (FRMS). We analyse the interaction of FRMS with the intra-cluster medium (ICM), in particular where, when and how the second generation of stars may form. From the results, we develop a timeline of the first approximately 40 Myr of GC evolution. The results of Paper I imply three phases during which the ICM is in a fundamentally different state, namely the wind bubble phase (lasting 3.5 to 8.8 Myr), the supernova phase (lasting 26.2 to 31.5 Myr), and the dark remnant accretion phase (lasting 0.1 to 4 Myr): (i) Quickly after the first generation massive stars have formed, stellar wind bubbles compress the ICM into thin filaments. No stars may form in the normal way during this phase, due to the high Lyman-Werner flux density. If the first generation massive stars have however equatorial ejections, as we proposed in the FRMS scenario, accretion may resume in the shadow of the equatorial ejecta. The second generation stars may then form due to gravitational instability in these discs that are fed by both the FRMS ejecta and pristine gas. [...]