Formation of Massive and Wide First-star Binaries in Radiation Hydrodynamic Simulations

Abstract

We study the formation of Population III stars by performing radiation hydrodynamic simulations for three different initial clouds extracted from cosmological hydrodynamic simulations. Starting from the cloud collapse stage, we follow the growth of protostars by accretion for ∼105 yr until the radiative feedback from the protostars suppresses the accretion and the stellar properties are nearly fixed. We find that Population III stars form in massive and wide binary/small-multiple stellar systems, with masses >30 M ⊙ and separations >2000 au. We also find that the properties of the final stellar system correlate with those of the initial clouds: the total mass increases with the cloud-scale accretion rate, and the angular momentum of the binary orbit matches that of the initial cloud. While the total mass of the system in our simulations is consistent with our previous single-star formation simulations, individual masses are lower due to mass sharing, suggesting potential modification in the extent of feedback from Population III stars in the subsequent evolution of the Universe. We also identify such systems as mini-binaries embedded in a wider outer multiple-star system, which could evolve into progenitors for observed gravitational wave events.

Zero Metallicity with Zero CPU Hours: Masses of the First Stars on the Laptop

“…Finally, although this work only considers the formation of the massive central star in each cloud, Liu et al (2020) found that the formation of Pop III star clusters by disk fragmentation can be described by simple scaling laws that capture the key trends in 3D hydrodynamic simulations of primordial starforming clouds. Our model can be generalized and improved to consider Pop III star clusters and self-shielding in aspherical accretion flows using the results of 3D radiative hydrodynamic simulations that follow the growth and feedback of multiple protostars (e.g., Sugimura et al 2020Sugimura et al , 2023Park et al 2023aPark et al , 2023b, which is an intriguing direction for future research.…”

“…The formation and evolution of protostars during disk fragmentation (e.g., growth by competing accretion, mergers, and ejections by gravitational scatters) are still poorly understood due to the limited resolution and/or time coverage of current simulations. It is likely that multiple protostars will survive and grow to comparable masses by the moment of cloud evaporation (Sugimura et al 2020(Sugimura et al , 2023Park et al 2023aPark et al , 2023b. In this case, the strength of ionization feedback will be overestimated by the assumption that the star-forming disk only feeds one central protostar, since the efficiency of producing ionizing photons increases with stellar mass.…”

Low-mass Population III Star Formation due to the HD Cooling Induced by Weak Lyman–Werner Radiation

“…A part of the dense region collapses and becomes Pop III star(s) because we artificially prevent structure formation above a specific density using the stiff-EOS technique to achieve long computation times. In addition, some physical processes occurring inside the core could cause differences between the core mass and stellar mass: a decrease by circumstellar disk fragmentation (e.g., Hirano & Bromm 2017;Susa 2019;Sugimura et al 2020Sugimura et al , 2023 and an increase by protostellar radiative feedback from high accretion rates (e.g., Hosokawa et al 2011;Hirano et al 2014;Hosokawa et al 2016).…”

Amplification and Saturation of Turbulent Magnetic Fields in Collapsing Primordial Gas Clouds

“…On the other hand, a number of recent numerical studies have indicated that the first stars are likely formed as multiple systems, such as a binary, triplet, etc. The multiple systems form through the fragmentation of the accretion disk, which emerges after the formation of the central protostar (Greif et al 2011(Greif et al , 2012Susa 2013Susa , 2019Susa et al 2014;Hirano & Bromm 2017;Inoue & Yoshida 2020;Sharda et al 2020Sharda et al , 2021Sugimura et al 2020Sugimura et al , 2023Chiaki & Yoshida 2022). Studying this fragmentation behavior is considered to be crucial for determining the initial mass function (IMF) of the first stars.…”

“…Turbulence and magnetic fields are fundamental physical phenomena in the study of disk fragmentation. For instance, disk fragmentation is promoted by turbulence (Clark et al 2011;Riaz et al 2018;Wollenberg et al 2020;Sugimura et al 2023) or suppressed by magnetic fields (Machida & Doi 2013;Sharda et al 2020;Sadanari et al 2021). The efficiency of these effects depends on the properties of the magnetic field (its strength and structure); therefore, investigating and clarifying their details are essential for the study of the first star formation.…”