GRMHD formulation of highly super-Chandrasekhar rotating magnetised white dwarfs: Stable configurations of non-spherical white dwarfs

TL;DR

This paper develops a general relativistic magnetohydrodynamic model to study highly super-Chandrasekhar rotating magnetised white dwarfs, revealing their potential stability and structure, and suggesting they could be progenitors of overluminous type Ia supernovae.

Contribution

It introduces a novel GRMHD framework for modeling rotating, magnetised white dwarfs and demonstrates the existence of stable super-Chandrasekhar configurations with specific magnetic and rotational properties.

Findings

White dwarfs with 2-3 solar masses are possible under strong magnetic fields and differential rotation.

Such white dwarfs could explain overluminous type Ia supernovae.

Polar hollows can form in certain stable configurations.

Abstract

Here we extend the exploration of significantly super-Chandrasekhar magnetised white dwarfs by numerically computing axisymmetric stationary equilibria of differentially rotating magnetised polytropic compact stars in general relativity (GR), within the ideal magnetohydrodynamic regime. We use a general relativistic magnetohydrodynamic (GRMHD) framework that describes rotating and magnetised axisymmetric white dwarfs, choosing appropriate rotation laws and magnetic field profiles (toroidal and poloidal). The numerical procedure for finding solutions in this framework uses the 3+1 formalism of numerical relativity, implemented in the open source XNS code. We construct equilibrium sequences by varying different physical quantities in turn, and highlight the plausible existence of super-Chandrasekhar white dwarfs, with masses in the range of 2-3 solar mass, with central (deep interior) magnetic fields of the order of $10^{14}$ Gauss and differential rotation with surface time periods of about 1-10 seconds. We note that such white dwarfs are candidates for the progenitors of peculiar, overluminous type Ia supernovae, to which observational evidence ascribes mass in the range 2.1-2.8 solar mass. We also present some interesting results related to the structure of such white dwarfs, especially the existence of polar hollows in special cases.