Probing Strong Field $f(R)$ Gravity and Ultra-Dense Matter with the Structure and Thermal Evolution of Neutron Stars

Abstract

Thermal evolution of neutron stars is studied in the $f(R)=R+\alpha R^2$ theory of gravity. We first describe the equations of stellar structure and evolution for a spherically symmetric spacetime plus a perfect fluid at rest. We then present numerical results for the structure of neutron stars using four nucleonic dense matter equations of state and a series of gravity theories for $\alpha$ ranging from zero, i.e., General Relativity, up to $\alpha \approx 10^{16}$ cm${}^2$. We emphasize properties of these neutron star models that are of relevance for their thermal evolution as the threshold masses for enhanced neutrino emission by the direct Urca process, the proper volume of the stellar cores where this neutrino emission is allowed, the crust thickness, and the surface gravitational acceleration that directly impact the observable effective temperature. Finally, we numerically solve the equations of thermal evolution and explicitly analyze the effects of altering gravity. We find that uncertainties in the dense matter microphysics, as the core chemical composition and superfluidity/superconductivity properties, as well as the astrophysical uncertainties on the chemical composition of the surface layers, have a much stronger impact than possible modifications of gravity within the studied family of $f(R)$ theories. We conclude that within this family of gravity theories, conclusions from previous studies of neutron star thermal evolution are not significantly altered by alteration of gravity. Conversely, this implies that neutron star cooling modeling may not be a useful tool to constrain deviations of gravity from Einstein theory unless these are much more radical than in the $f(R)=R+\alpha R^2$ framework.

22 pages, 16 figures

References in corpus (39)

• Unified cosmic history in modified gravity: from F(R) theory to Lorentz non-invariant models
• Shapiro delay measurement of a two solar mass neutron star
• A Massive Pulsar in a Compact Relativistic Binary
• Rapid Cooling of the Neutron Star in Cassiopeia A Triggered by Neutron Superfluidity in Dense Matter
• Hydrostatic equilibrium and stellar structure in f(R)-gravity
• The Expansion Asymmetry and Age of the Cassiopeia A Supernova Remnant
• Extreme neutron stars from Extended Theories of Gravity
• Neutron Stars and the Nuclear Equation of State
• A Singularity Problem with f(R) Dark Energy
• Dense Matter in Compact Stars: Theoretical Developments and Observational Constraints
• Strongly paired fermions: Cold atoms and neutron matter
• Relativistic stars in f(R) gravity, and absence thereof
• Extended Gravity Description for the GW190814 Supermassive Neutron Star
• Slowly rotating neutron and strange stars in $R^2$ gravity
• The existence of relativistic stars in f(R) gravity
• Cooling of Neutron Stars. Hadronic Model
• Thermal luminosities of cooling neutron stars
• Annual modulation results from three-year exposure of ANAIS-112
• Structure of neutron stars in R-squared gravity
• High angular resolution ALMA images of dust and molecules in the SN 1987A ejecta
• Magnetic Neutron Stars in f(R) gravity
• Rapidly rotating neutron stars in $R$-squared gravity
• Cooling of Accretion-Heated Neutron Stars
• Theory of gravitation theories: a no-progress report
• Robust approach to f(R) gravity
• The Cauchy problem of f(R) gravity
• NS 1987A in SN 1987A
• Statistical theory of thermal evolution of neutron stars
• Constraining the Neutron Star Mass--Radius Relation and Dense Matter Equation of State with NICER. III. Model Description and Verification of Parameter Estimation Codes
• A lower limit on the heat capacity of the neutron star core
• Diffusive nuclear burning in cooling simulations and application to new temperature data of the Cassiopeia A neutron star
• Statistical theory of thermal evolution of neutron stars - II. Limitations on direct Urca threshold
• Dark matter as a Weyl geometric effect
• The neutron star soft X-ray transient 1H1905+000 in quiescence
• The cooling of the Central Compact Object in Cas A from 2006 to 2020
• The matter Lagrangian of an ideal fluid
• Model-independent constraints on superfluidity from the cooling neutron star in Cassiopeia A
• Neutron Stars in frames of $R^2$-gravity and Gravitational Waves
• Constraining the properties of dense neutron star cores: The case of the low-mass X-ray binary HETE J1900.1-2455

Cited by in corpus (2)

• Compact star in noninteger power model of $f(R)$ gravity
• Solar system tests and neutron stars in $f(R)$ gravity revisited