Variable Accretion Rates and Fluffy First Stars

TL;DR

This paper investigates how variable accretion rates affect the evolution of primordial protostars, revealing they are extended 'fluffy' objects that may merge or form tight binaries, influencing early star cluster dynamics and gamma-ray burst progenitors.

Contribution

It combines hydrodynamical simulations with stellar evolution models to study the impact of variable accretion on Population III protostars, highlighting their extended radii and potential for mergers and binary formation.

Findings

Primordial protostars are extended 'fluffy' objects during most of their pre-main-sequence phase.

High accretion luminosity feedback has minimal impact on star cluster evolution.

Close encounters and extended radii suggest mergers and formation of massive tight binaries.

Abstract

We combine the output of hydrodynamical simulations of Population III star cluster formation with stellar evolution models, and calculate the evolution of protostars experiencing variable mass accretion rates due to interactions within a massive disk. We find that the primordial protostars are extended 'fluffy' objects for the bulk of their pre-main-sequence lifetimes. Accretion luminosity feedback from such objects is high, but as shown in previous work, has a minimal effect on the star cluster. The extended radii of the protostars, combined with the observation of close encounters in the simulations, suggests that mergers will occur in such systems. Furthermore, mass transfer between close protostellar binaries with extended radii could lead to massive tight binaries, which are a possible progenitor of gamma ray bursts.