Toward $ab\,initio$ extremely metal poor stars

TL;DR

This paper presents a detailed simulation of the formation of the first metal-enriched stars from Population III supernovae, revealing that such stars can form at extremely low metallicities from surviving primordial clouds.

Contribution

It provides the most realistic simulation to date of the pathway to the first metal-enriched stars, including radiative and supernova feedback from a Population III star.

Findings

First metal-enriched stars can form at metallicities of 2-5×10⁻⁴ Z_⊙.

Supernova metals deposit superficially on primordial clouds, not uniformly.

Surviving primordial clouds can collapse to form metal-poor stars with elliptical orbits.

Abstract

Extremely metal poor stars have been the focus of much recent attention owing to the expectation that their chemical abundances can shed light on the metal and dust yields of the earliest supernovae. We present our most realistic simulation to date of the astrophysical pathway to the first metal enriched stars. We simulate the radiative and supernova hydrodynamic feedback of a $60\,M_\odot$ Population III star starting from cosmological initial conditions realizing Gaussian density fluctuations. We follow the gravitational hydrodynamics of the supernova remnant at high spatial resolution through its freely-expanding, adiabatic, and radiative phases, until gas, now metal-enriched, has resumed runaway gravitational collapse. Our findings are surprising: while the Population III progenitor exploded with a low energy of $10^{51}\,\text{erg}$ and injected an ample metal mass of $6\,M_\odot$, the first cloud to collapse after the supernova explosion is a dense surviving primordial cloud on which the supernova blastwave deposited metals only superficially, in a thin, unresolved layer. The first metal-enriched stars can form at a very low metallicity, of only $2-5\times10^{-4}\,Z_\odot$, and can inherit the parent cloud's highly elliptical, radially extended orbit in the dark matter gravitational potential.