Constraining neutron star properties and dark matter admixture with the NITR-I equation of state: Insights from observations and universal relations

Abstract

A recent observational study has constrained the maximum mass of neutron stars (NSs), with particular attention to PSR J0952-0607 and the compact star remnant HESS J1731-347, especially in the low-mass regime. Building on our earlier work, which developed the NITR energy density functional (EDF) to reproduce the mass limit of PSR J0952-0607 but did not satisfy other observational constraints, this study introduces a refined EDF named ``NITR-I". NITR-I successfully reconciles the PSR J0952-0607 mass limit with observational data, including radius measurements from NICER+XMM and tidal deformability constraints from GW170817, demonstrating its robustness. The low-mass constraint associated with HESS J1731-347 indicates diverse NS compositions. Since NITR-I alone cannot satisfy this constraint, we explore the role of dark matter (DM) within NSs to bridge the gap. Incorporating DM, particularly at specific Fermi momentum values, enables the model to address this constraint. We further analyze the influence of DM on various NS properties, such as tidal deformability and non-radial $f$-mode oscillations, across multiple relativistic mean-field models. The presence of DM suggests a reduction in tidal deformability and shifts in oscillation frequencies, potentially offering detectable signatures in gravitational wave observations from neutron star mergers. Additionally, we investigate universal relations (URs) for DM-admixed NSs, focusing on correlations such as compactness versus tidal deformability and $f$-mode frequency versus tidal deformability. Canonical values for these properties are estimated using GW170817 data, offering further insights into the structure and composition of neutron stars.

Figures (9)

• Figure 1: (a) The EOS for the NITR-I model is displayed and compared alongside with NITR model. The low-density constraint by the chiral Effective Field Theory (EFT) is also shown Drischler_2021. (b) The sound speed ($C_s^2$) as a function of the baryon density.
• Figure 2: (a) The mass-radius profiles of the NS are shown forNITR-I and NITR EOSs with various observational constraints such as recently observed heaviest pulsar PSR J0952-0607 Romani_2022, HESS J1731-347 HESS_2022 and NICER+XMM data Miller_2021. (b) The tidal deformability is plotted as a function of the mass, including with the constraint from GW170817 event Abbott_2018.
• Figure 3: The mass-radius profiles are shown with and without DM by varying $k_f^{\rm DM}$. The color bands represent the mass range of different pulsars such as PSR J0952-0607 Romani_2022, PSR J0740+6620 Cromartie_2020. The black error bars represent the radii limits for the canonical star and $2.08 \ M_\odot$ star reported by NICER+XMM data Miller_2021. The 1$\sigma$ and 2$\sigma$ contours of HESS J1731-347 HESS_2022 are represented by dashed lines and solid lines, respectively, in the contour.
• Figure 4: Left: Variation of the tidal deformability with mass for both with and without DM is shown, and the observational constraint for GW170817 Abbott_2018 is also imposed. The blue-shaded region corresponds to the constraints derived from the GW170817 measurements Abbott_2018. Right: The non-radial $f$-mode frequency is shown as a function of the mass of the NS with different DM configurations. For both panels, the DM configurations are represented as $k_f^{\rm DM}=0.0 \ {\rm (solid \ line)}, \ 0.02 \ {\rm (dashed \ line) \ {\rm and} \ 0.03 \ {\rm GeV} \ {\rm (dotted \ line)}}$.
• Figure 5: The $f$-mode frequency is fitted with the average density of the star using the Eq. \ref{['eq:fit_f-n']}. The best fit for our results with various DM configurations is represented by the black solid line in each panel, which we also compare with the previous works, including AK Fit Andersson-Kokkotas_GW_1996, PC Fit Bikram_2021-fmode, and HCD Fit Das_fmode_2021.