Carbon-oxygen ultra-massive white dwarfs in general relativity

TL;DR

This study models ultra-massive white dwarfs with masses over 1.29 Msun using general relativity, revealing significant impacts on their structure, evolution, and pulsations, especially near the stability limit.

Contribution

First to incorporate full general relativity effects into evolutionary and pulsational models of ultra-massive white dwarfs above 1.29 Msun.

Findings

White dwarfs >1.382 Msun become gravitationally unstable due to relativity.

Relativistic effects cause smaller radii and altered pulsation properties in massive white dwarfs.

General relativity significantly influences the evolution and pulsations of white dwarfs above 1.30 Msun.

Abstract

We employ the La Plata stellar evolution code, LPCODE, to compute the first set of constant rest-mass carbon-oxygen ultra-massive white dwarf evolutionary sequences for masses higher than 1.29 Msun that fully take into account the effects of general relativity on their structural and evolutionary properties. In addition, we employ the LP-PUL pulsation code to compute adiabatic g-mode Newtonian pulsations on our fully relativistic equilibrium white dwarf models. We find that carbon-oxygen white dwarfs more massive than 1.382 Msun become gravitationally unstable with respect to general relativity effects, being this limit higher than the 1.369 Msun we found for oxygen-neon white dwarfs. As the stellar mass approaches the limiting mass value, the stellar radius becomes substantially smaller compared with the Newtonian models. Also, the thermo-mechanical and evolutionary properties of the most massive white dwarfs are strongly affected by general relativity effects. We also provide magnitudes for our cooling sequences in different passbands. Finally, we explore for the first time the pulsational properties of relativistic ultra-massive white dwarfs and find that the period spacings and oscillation kinetic energies are strongly affected in the case of most massive white dwarfs. We conclude that the general relativity effects should be taken into account for an accurate assessment of the structural, evolutionary, and pulsational properties of white dwarfs with masses above 1.30 Msun.