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In-Stabilities of massive white dwarfs in modified gravity

Ronaldo V. Lobato, Geanderson A. Carvalho, Neelima G. Kelkar, Marek Nowakowski

TL;DR

This work addresses whether modified gravity can produce super-Chandrasekhar white dwarfs by solving GR and $f(R,L_m)$-gravity hydrostatic equations with a realistic Hamada–Salpeter EoS. It combines TOV-like structure equations with radial-stability analysis and explicitly includes nuclear instabilities from inverse $\beta$-decay and pycnonuclear reactions, which set density thresholds that can cap mass before gravitational instability. The results show that while the $f(R,L_m)$ parameter $\sigma$ can increase maximum masses for light elements, nuclear instabilities dictate stringent caps (e.g., $\sim1.6\,M_\odot$ for $^{16}$O), and for heavier nuclei the effect is even weaker; Fe remains largely unaffected. This underscores that realistic microphysics must be incorporated when assessing WD masses in modified gravity, constraining SN Ia progenitor scenarios in these theories.

Abstract

Super-Chandrasekhar white dwarfs are a timely topic in the last years in the scientific community due to its connection to supernovae type Ia (SN Ia). Some early studies tackled the possibility of white dwarfs surpassing the Chandrasekhar limit by means of a magnetic field. More recently, modified gravity has been highlighted as the reason for these stars to surpass the Chandrasekhar limit and becoming a supernova progenitor. However, in general simple assumptions are considered for the stellar structure and equation of state (EoS), which can lead to unreliable conclusions. In this work, we want to be rigorous and consider a realistic EoS to describe the white dwarfs in general relativity and modified gravity, taking into account nuclear instabilities that limit the maximum mass.

In-Stabilities of massive white dwarfs in modified gravity

TL;DR

This work addresses whether modified gravity can produce super-Chandrasekhar white dwarfs by solving GR and -gravity hydrostatic equations with a realistic Hamada–Salpeter EoS. It combines TOV-like structure equations with radial-stability analysis and explicitly includes nuclear instabilities from inverse -decay and pycnonuclear reactions, which set density thresholds that can cap mass before gravitational instability. The results show that while the parameter can increase maximum masses for light elements, nuclear instabilities dictate stringent caps (e.g., for O), and for heavier nuclei the effect is even weaker; Fe remains largely unaffected. This underscores that realistic microphysics must be incorporated when assessing WD masses in modified gravity, constraining SN Ia progenitor scenarios in these theories.

Abstract

Super-Chandrasekhar white dwarfs are a timely topic in the last years in the scientific community due to its connection to supernovae type Ia (SN Ia). Some early studies tackled the possibility of white dwarfs surpassing the Chandrasekhar limit by means of a magnetic field. More recently, modified gravity has been highlighted as the reason for these stars to surpass the Chandrasekhar limit and becoming a supernova progenitor. However, in general simple assumptions are considered for the stellar structure and equation of state (EoS), which can lead to unreliable conclusions. In this work, we want to be rigorous and consider a realistic EoS to describe the white dwarfs in general relativity and modified gravity, taking into account nuclear instabilities that limit the maximum mass.
Paper Structure (9 sections, 20 equations, 4 figures, 1 table)

This paper contains 9 sections, 20 equations, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Hydrostatic equilibrium
  3. Stability criteria for critical mass
  4. Gravitational instability
  5. Nuclear instabilities
  6. Inverse $\beta$-decay
  7. Pycnonuclear reaction
  8. Results and discussions
  9. Concluding remarks

Figures (4)

  • Figure 1: White dwarfs with different EoS within general relativity.
  • Figure 2: $^4$He white dwarfs within $f(\mathtt{R,L_m})$ gravity.
  • Figure 3: $^{16}$O white dwarfs within $f(\mathtt{R,L_m})$ gravity.
  • Figure 4: $^{56}$Fe white dwarfs within $f(\mathtt{R,L_m})$ gravity.