Understanding the Oldest White Dwarfs: Atmospheres of Cool WDs as Extreme Physics Laboratories

TL;DR

This paper uses advanced ab initio computational methods to study the atmospheres of old, helium-rich white dwarfs, revealing their extreme physical conditions and improving models for stellar evolution and cosmochronology.

Contribution

It introduces first-principles quantum mechanical calculations to model dense white dwarf atmospheres, a novel approach for understanding their properties under extreme conditions.

Findings

Stability and opacity of H- in dense helium clarified

Insights into C2 behavior in high-density atmospheres

Implications for white dwarf cooling and evolution models

Abstract

Reliable modeling of the atmospheres of cool white dwarfs is crucial for understanding the atmospheric evolution of these stars and for accurate white dwarfs cosmochronology. Over the last decade {\it ab initio} modeling entered many research fields and has been successful in predicting properties of various materials under extreme conditions. In many cases the investigated physical regimes are difficult or even impossible to access by experimental methods, and first principles quantum mechanical calculations are the only tools available for investigation. Using modern methods of computational chemistry and physics we investigate the atmospheres of helium-rich, old white dwarfs. Such atmospheres reach extreme, fluid like densities (up to grams per cm$^3$) and represent an excellent laboratory for high temperature and pressure physics and chemistry. We show our results for the stability and opacity of $\rm H^-$ and $\rm C_2$ in dense helium and the implications of our work for understanding cool white dwarfs.