Radiation Hydrodynamical Instabilities in Cosmological and Galactic Ionization Fronts

TL;DR

This paper uses advanced 3D radiation hydrodynamical simulations to show that the ionization fronts of the first stars and galaxies were unstable, influencing early universe evolution and star formation.

Contribution

It introduces a novel adaptive multistep integration scheme for self-consistent cosmological and galactic ionization front simulations.

Findings

I-fronts were prone to violent instabilities.

Instabilities enhanced UV photon escape into the IGM.

Clumpy media formed, aiding early supernovae and star formation.

Abstract

Ionization fronts, the sharp radiation fronts behind which H/He ionizing photons from massive stars and galaxies propagate through space, were ubiquitous in the universe from its earliest times. The cosmic dark ages ended with the formation of the first primeval stars and galaxies a few hundred Myr after the Big Bang. Numerical simulations suggest that stars in this era were very massive, 25 - 500 solar masses, with H II regions of up to 30,000 light-years in diameter. We present three-dimensional radiation hydrodynamical calculations that reveal that the I-fronts of the first stars and galaxies were prone to violent instabilities, enhancing the escape of UV photons into the early intergalactic medium (IGM) and forming clumpy media in which supernovae later exploded. The enrichment of such clumps with metals by the first supernovae may have led to the prompt formation of a second generation of low-mass stars, profoundly transforming the nature of the first protogalaxies. Cosmological radiation hydrodynamics is unique because ionizing photons coupled strongly to both gas flows and primordial chemistry at early epochs, introducing a hierarchy of disparate characteristic timescales whose relative magnitudes can vary greatly throughout a given calculation. We describe the adaptive multistep integration scheme we have developed for the self-consistent transport of both cosmological and galactic ionization fronts.