A perturbation study of axisymmetric strongly magnetic degenerate stars : the case of super-Chandrasekhar white dwarfs

TL;DR

This study investigates the stability of strongly magnetized, super-Chandrasekhar white dwarfs and finds that such configurations are inherently unstable, challenging their role as progenitors of over-luminous Type-Ia supernovae.

Contribution

The paper provides the first linear and non-linear perturbation analysis demonstrating the instability of axisymmetric, magnetically supported super-Chandrasekhar white dwarfs.

Findings

Magnetically supported white dwarfs are unstable within an Alfvén crossing time.

Uniform rotation cannot stabilize these super-massive configurations.

Long-lived super-Chandrasekhar white dwarfs supported by magnetic fields are unlikely in nature.

Abstract

In the presence of a strong magnetic field a stellar equilibrium configuration, aided by the Lorentz force, can support a larger mass than a non-magnetic one. This has been considered a possible explanation of the super-Chandrasekhar mass white dwarfs giving rise to over-luminous Type-Ia supernovae. We present here linear and non-linear perturbation studies of such strongly magetised configurations and show that axisymmetric configurations with poloidal or toroidal fields are unstable. The numerical evolution of the perturbations shows instability after about an Alfv\'en crossing time. This time scale is very short for the magnetically supported super-Chandrasekhar mass white dwarfs. Uniform rotation about the symmetry axis can reduce the growth rate but can not stabilize the super-massive configurations. It is concluded that long-lived super-Chandrasekhar mass white dwarfs supported by magnetic field are unlikely to occur in Nature.