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Effects of Dark Matter on the Spontaneous Scalarization in Neutron Stars

Fahimeh Rahimi, Zeinab Rezaei

TL;DR

This paper investigates how dark matter captured in neutron stars influences spontaneous scalarization in scalar-tensor gravity. By employing two distinct dark-matter equations of state—pseudo-isothermal and self-interacting fermionic DM—the authors solve for dark-matter admixed neutron-star structures within an Einstein-frame scalar-tensor framework and analyze the central scalar field, scalar charge, and mass–radius relations. They find that dark matter pressure can both enhance scalarization and shift observable properties, with the effects depending on the DM EoS and coupling parameter, and they show that certain observed systems like GW170817 and 4U 1820-30 can be accommodated as scalarized DM-admixed neutron stars. Overall, the results suggest DM properties leave imprints on scalarized neutron stars, offering a potential astrophysical probe of DM in the context of alternative gravity theories.

Abstract

Dark matter, an important portion of compact objects, can influence different phenomena in neutron stars. The spontaneous scalarization in the scalar-tensor gravity has been proposed for neutron stars. Here, we investigate the spontaneous scalarization in dark matter admixed neutron stars. Applying the dark matter equations of state, we calculate the structure of scalarized neutron stars containing dark matter. The dark matter equations of state are based on observational data from the rotational curves of galaxies and the fermionic self-interacting dark matter. Our results verify that the spontaneous scalarization is affected by the dark matter pressure in neutron stars. Depending on the central density of scalarized dark matter admixed neutron stars, the dark matter pressure alters the central scalar field. The increase of dark matter pressure in low-density scalarized stars amplifies the central scalar field. However, the pressure of dark matter in high-density scalarized stars suppresses the central scalar field. Our calculations confirm that the stars in the merger event GW170817 and in the low-mass X-ray binary 4U 1820-30 can be scalarized dark matter admixed neutron stars.

Effects of Dark Matter on the Spontaneous Scalarization in Neutron Stars

TL;DR

This paper investigates how dark matter captured in neutron stars influences spontaneous scalarization in scalar-tensor gravity. By employing two distinct dark-matter equations of state—pseudo-isothermal and self-interacting fermionic DM—the authors solve for dark-matter admixed neutron-star structures within an Einstein-frame scalar-tensor framework and analyze the central scalar field, scalar charge, and mass–radius relations. They find that dark matter pressure can both enhance scalarization and shift observable properties, with the effects depending on the DM EoS and coupling parameter, and they show that certain observed systems like GW170817 and 4U 1820-30 can be accommodated as scalarized DM-admixed neutron stars. Overall, the results suggest DM properties leave imprints on scalarized neutron stars, offering a potential astrophysical probe of DM in the context of alternative gravity theories.

Abstract

Dark matter, an important portion of compact objects, can influence different phenomena in neutron stars. The spontaneous scalarization in the scalar-tensor gravity has been proposed for neutron stars. Here, we investigate the spontaneous scalarization in dark matter admixed neutron stars. Applying the dark matter equations of state, we calculate the structure of scalarized neutron stars containing dark matter. The dark matter equations of state are based on observational data from the rotational curves of galaxies and the fermionic self-interacting dark matter. Our results verify that the spontaneous scalarization is affected by the dark matter pressure in neutron stars. Depending on the central density of scalarized dark matter admixed neutron stars, the dark matter pressure alters the central scalar field. The increase of dark matter pressure in low-density scalarized stars amplifies the central scalar field. However, the pressure of dark matter in high-density scalarized stars suppresses the central scalar field. Our calculations confirm that the stars in the merger event GW170817 and in the low-mass X-ray binary 4U 1820-30 can be scalarized dark matter admixed neutron stars.
Paper Structure (10 sections, 18 equations, 11 figures, 2 tables)

This paper contains 10 sections, 18 equations, 11 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Dark Matter Equations of State
  3. Dark Matter Admixed Neutron Stars in Scalar Tensor Gravity
  4. Results and Discussion
  5. Mass versus the central density of dark matter admixed neutron star
  6. Mass-radius relation of dark matter admixed neutron star
  7. Central scalar field of dark matter admixed neutron star
  8. Scalar charge in dark matter admixed neutron star
  9. Critical density of scalarization in dark matter admixed neutron star
  10. SUMMARY AND CONCLUDING REMARKS

Figures (11)

  • Figure 1: Left: Dark matter equation of state in the first model considering $\rho_g=0.2\times10^{16}g/cm^3$ and different values of $p_g$. In this figure and all following figures, $p_g$ is in units of $10^{35} dyn/cm^2$. Right: Dark matter equation of state in the second model with the mass $m=1 \ GeV$ and different values of the interaction between particles, $m_I$. We have assumed $\rho_0=1.66\times10^{14}g/cm^3$.
  • Figure 2: Neutron star matter equation of state constrained by the observational data Jiang.
  • Figure 3: Mass as a function of the central density, $\tilde{\rho}_{c}$, for neutron star (NS) and dark matter admixed neutron star (DMANS) in the first model of DM EoS considering the scalar-tensor theory (STT) with different values of the coupling constant, $\beta$. The results of the general theory of relativity (GR) are also presented.
  • Figure 4: Same as Figure \ref{['mro1']} but for the second model of DM EoS.
  • Figure 5: Mass versus the radius for NS and DMANS in the first model of DM EoS in GR and STT with different values of the coupling constant, $\beta$. Observational constraints on the mass and radius of NS are also given. The constraints are related to EXO 1745-248, 4U 1820-30, GW170817, and PSR J0030+0451. For more details, see the text.
  • ...and 6 more figures