Strongly Magnetized White Dwarfs and Their Instability Due to Nuclear Processes

Abstract

In this work, we study the properties of strongly magnetized white dwarfs (WDs), taking into account the electron capture and pycnonuclear fusion reactions instabilities. The structure of WDs is obtained by solving the Einstein–Maxwell equations with a poloidal magnetic field in a fully general relativistic treatment. The stellar fluid is assumed to be composed of a regular crystal lattice made of carbon ions immersed in a degenerate relativistic electron gas. The onset of electron capture reactions and pycnonuclear reactions are determined with and without magnetic fields. We find that magnetized WDs significantly exceed the standard Chandrasekhar mass limit, even when electron capture and pycnonuclear fusion reactions are present in the stellar interior. We obtain a maximum white dwarf mass of around 2.14 M ⊙ for a central magnetic field of ∼3.85 × 10 14 G, which indicates that magnetized WDs may play a crucial role for the interpretation of superluminous type Ia supernovae. Furthermore, we show that the critical density for pycnonuclear fusion reactions limits the central white dwarf density to 9.35 × 10 9 g cm −3 . As a consequence, equatorial radii of WDs cannot be smaller than ∼1100 km. Another interesting feature concerns the relationship between the central stellar density and the strength of the magnetic field at the core of a magnetized white dwarf. For high magnetic fields, we find that the central density increases (stellar radius decrease) with magnetic field strength, which makes highly magnetized WDs more compact. The situation is reversed if the central magnetic field is less than ∼10 13 G.