The formation of protostellar binaries in primordial minihalos

TL;DR

This study uses advanced simulations to investigate how primordial gas clouds collapse and fragment into binary star systems, revealing dependencies on turbulence and rotation that influence the properties of early universe binaries.

Contribution

It introduces a combined SPH and astrochemistry simulation framework to quantify the formation and properties of Pop III binary systems in primordial minihalos, highlighting the effects of turbulence and rotation.

Findings

Fragmentation depends strongly on turbulence and rotation.

Multiple Pop III proto-binaries formed with diverse mass ratios.

Mass accretion rates vary from 2.18e-4 to 2.31e-1 M_sun/yr.

Abstract

The first stars are known to form in primordial gas, either in minihalos with about $10^6$~M$_\odot$ or so-called atomic cooling halos of about $10^8$~M$_\odot$. Simulations have shown that gravitational collapse and disk formation in primordial gas yield dense stellar clusters. In this paper, we focus particularly on the formation of protostellar binary systems, and aim to quantify their properties during the early stage of their evolution. For this purpose, we combine the smoothed particle hydrodynamics code GRADSPH with the astrochemistry package KROME. The GRADSPH-KROME framework is employed to investigate the collapse of primordial clouds in the high-density regime, exploring the fragmentation process and the formation of binary systems. We observe a strong dependence of fragmentation on the strength of the turbulent Mach number $\mathcal{M}$ and the rotational support parameter $\beta{}$. Rotating clouds show significant fragmentation, and have produced several Pop.~III proto-binary systems. We report maximum and minimum mass accretion rates of $2.31 \times 10^{-1}$~M$_{\odot}$ yr$^{-1}$ and $2.18\times 10^{-4}$~M$_{\odot}$ yr$^{-1}$. The mass spectrum of the individual Pop III proto-binary components ranges from $0.88$~M$_{\odot}$ to $31.96$~M$_{\odot}$ and has a sensitive dependence on the Mach number $\mathcal{M}$ as well as on the rotational parameter $\beta{}$. We also report a range from $\sim0.01$ to $\sim1$ for the mass ratio of our proto-binary systems.