Low-mass star formation triggered by early supernova explosions

TL;DR

This paper models how early supernova explosions can trigger the formation of low-mass, extremely metal-poor stars in the early universe through shell fragmentation and cooling processes.

Contribution

It introduces a new model demonstrating that early supernova remnants can induce low-mass star formation in metal-poor environments via shell fragmentation.

Findings

Supernova remnants undergo efficient cooling and become gravitationally unstable.

Cooling by dust leads to rapid temperature decline and fragmentation.

The model supports the formation of low-mass stars in extremely metal-poor conditions.

Abstract

We study the formation of low-mass and extremely metal-poor stars in the early universe. Our study is motivated by the recent discovery of a low-mass (M < 0.8 Msun) and extremely metal-poor (Z <= 4.5 x 10^{-5} Zsun) star in the Galactic halo by Caffau et al. We propose a model that early supernova (SN) explosions trigger the formation of low-mass stars via shell fragmentation. We first perform one-dimensional hydrodynamic simulations of the evolution of an early SN remnant. We show that the shocked shell undergoes efficient radiative cooling and then becomes gravitationally unstable to fragment and collapse in about ten million years. We then follow the thermal evolution of the collapsing fragments using a one-zone code. Our one-zone calculation treats chemistry and radiative cooling self-consistently in low-metallicity gas. The collapsing gas cloud evolves roughly isothermally, until it cools rapidly by dust continuum emission at the density 10^{13}-10^{14} /cc. The cloud core then becomes thermally and gravitationally unstable and fragments. We argue that early SNe can trigger the formation of low-mass stars in the extremely metal-poor environment as Caffau et al. discovered recently.