Constraining the Statistics of Population III Binaries

TL;DR

This study uses cosmological simulations to analyze the formation, characteristics, and binary properties of Population III stars in early minihalo environments, revealing a high binary fraction and diverse orbital features.

Contribution

It provides the first detailed analysis of binary properties of Pop III stars in cosmological simulations, including binary fraction, orbital parameters, and merger/ejection rates.

Findings

Binary fraction of ~36% among Pop III systems

Semi-major axes up to 3000 AU observed

Approximately 50% of sink particles are ejected or merged

Abstract

We perform a cosmological simulation in order to model the growth and evolution of Population III (Pop III) stellar systems in a range of host minihalo environments. A Pop III multiple system forms in each of the ten minihaloes, and the overall mass function is top-heavy compared to the currently observed initial mass function in the Milky Way. Using a sink particle to represent each growing protostar, we examine the binary characteristics of the multiple systems, resolving orbits on scales as small as 20 AU. We find a binary fraction of ~36%, with semi-major axes as large as 3000 AU. The distribution of orbital periods is slightly peaked at < 900 yr, while the distribution of mass ratios is relatively flat. Of all sink particles formed within the ten minihaloes, ~50% are lost to mergers with larger sinks, and ~50% of the remaining sinks are ejected from their star-forming disks. The large binary fraction may have important implications for Pop III evolution and nucleosynthesis, as well as the final fate of the first stars.