Electron Captures and Stability of White Dwarfs

TL;DR

This paper reviews how electron captures and magnetic fields influence white dwarf stability, deriving new formulas for threshold densities and analyzing their effects on stellar structure.

Contribution

It introduces new analytical formulas for threshold densities of electron captures in magnetic fields and examines their impact on white dwarf stability and structure.

Findings

Magnetic fields significantly alter electron capture thresholds.

New formulas improve estimates of white dwarf stability limits.

Magnetic effects can influence super-Chandrasekhar white dwarf models.

Abstract

Electron captures by atomic nuclei in dense matter are among the most important processes governing the late evolution of stars, limiting in particular the stability of white dwarfs. Despite considerable progress in the determination of the equation of state of dense Coulomb plasmas, the threshold electron Fermi energies are still generally estimated from the corresponding $Q$ values in vacuum. Moreover, most studies have focused on nonmagnetized matter. However, some white dwarfs are endowed with magnetic fields reaching $10^9$ G. Even more extreme magnetic fields might exist in super Chandrasekhar white dwarfs, the progenitors of overluminous type Ia supernovae like SN 2006gz and SN 2009dc. The roles of the dense stellar medium and magnetic fields on the onset of electron captures and on the structure of white dwarfs are briefly reviewed. New analytical formulas are derived to evaluate the threshold density for the onset of electron captures for arbitrary magnetic fields. Their influence on the structure of white dwarfs is illustrated by simple analytical formulas and numerical calculations.