The Effects of Accretion Luminosity upon Fragmentation in the Early Universe

TL;DR

This study introduces a new method to include accretion luminosity in simulations of primordial star formation, revealing its delaying effect on fragmentation but limited influence on overall protostar growth due to dynamical interactions.

Contribution

The paper presents a novel prescription for accretion luminosity in smoothed particle hydrodynamics simulations of early universe star formation.

Findings

Accretion luminosity delays but does not prevent fragmentation.

Dynamical interactions dominate protostar accretion and ejections.

Inner disk accretion rates are highly variable, unlike simplified models.

Abstract

We introduce a prescription for the luminosity from accreting protostars into smoothed particle hydrodynamics simulation, and apply the method to simulations of five primordial minihalos generated from cosmological initial conditions. We find that accretion luminosity delays fragmentation within the halos, but does not prevent it. In halos that slowly form a low number of protostars, the accretion luminosity can reduce the number of fragments that are formed before the protostars start ionising their surroundings. However, halos that rapidly form many protostars become dominated by dynamical processes, and the effect of accretion luminosity becomes negligible. Generally the fragmentation found in the halos is highly dependent on the initial conditions. Accretion luminosity does not substantially affect the accretion rates experienced by the protostars, and is far less important than dynamical interactions, which can lead to ejections that effectively terminate the accretion. We find that the accretion rates onto the inner regions of the disks (20 AU) around the protostars are highly variable, in contrast to the constant or smoothly decreasing accretion rates currently used in models of the pre-main sequence evolution of Population III stars.