Influence of Fermionic Dark Matter on the Structural and Tidal Properties of Neutron Stars

TL;DR

The paper investigates how fermionic dark matter (DM) affects neutron star structure and tides by modeling DM as a zero-temperature ideal Fermi gas within a gravitationally coupled two-fluid framework, with DM mass fraction $f$ and particle mass $\\mu$. Using four realistic NM EOSs (SLy, MPA1, ENG, AP3) and the DM EOS parameterized by $\\mu$ and $f$, the study solves the two-fluid TOV equations and computes tidal metrics such as the tidal Love number $k_2$ and the dimensionless deformability $\\Lambda$. The results show that $M$, $R$, $\\Lambda$, and $k_2$ depend sensitively on $\\mu$, $f$, and NM stiffness, with higher $\\mu$ and $f$ generally softening the effective EOS and reducing $\\Lambda$, though some stiff NM cases with moderate $f$ can be consistent with NICER and GW170817 constraints. The work also reveals DM-core to DM-halo transitions as $f$ varies and highlights the need to include DM–DM interactions in future Bayesian analyses to tighten DM parameter constraints from observations.

Abstract

The inclusion of dark matter (DM) in the modeling of neutron stars (NSs) provides important information about the properties of DM and the nature of dense matter. Using some normal matter realistic equation of states (EOSs)with ideal Fermi gas DM EOS in a two-fluid framework, we systematically investigate the observable properties of dark matter-admixed neutron stars with an arbitrary dark matter mass fraction (f) and dark matter particle mass ($μ$). It has been observed that the deviations of these observable properties from pure normal matter behavior depend significantly on the amount of f,$μ$ value, and stiffness of normal matter EOS. Furthermore, it has been noted that the properties of dark matter admixed neutron stars are weakly constrained with recent observational constraints.

Figures (12)

• Figure 1: EOSs for various pure NM models and pure DM models at zero temperature.
• Figure 2: Mass as a function of radius of pure NM stars and pure DM stars with different masses corresponding to the EOSs shown in Fig. \ref{['fig:pressure_energy']}.The bands of different colors denote the accurate measurement of masses of some observed pulsarsantoniadis2013massivefonseca2021refinedromani2022psr.The black horizontal line indicates the span of neutron star radii at $1.4$$M_{\odot}$ is in between $11-13 \,km$.miller2021radiusriley2021nicer
• Figure 3: Dimensionless tidal deformability against mass for the EOSs shown in Fig. \ref{['fig:pressure_energy']}.The grey bar at $1.4\,M_{\odot}$ indicates observational constraints on $\Lambda$ from GW170817 for a $1.4\,M_{\odot}$ neutron star $\Lambda_{1.4\,M_{\odot}}\approx\,70-580$
• Figure 4: Tidal Love number against mass for the EOSs shown in Fig. \ref{['fig:pressure_energy']}.
• Figure 5: Mass-radius relations of dark matter admixed neutron stars using SLy equation of state with varying dark matter fractions $f$ and dark matter particle mass $\mu$ (in GeV). The results are compared against observational constraints from recent pulsar measurements.