Fermionic Dark Matter's Role in Shaping Anisotropic Neutron Stars

Recent research has explored the effects of fermionic dark matter (DM) interactions on the properties of anisotropic neutron stars (NS). The study, titled "Implications of Fermionic Dark Matter Interactions on Anisotropic Neutron Stars," was conducted by Premachand Mahapatra and colleagues and submitted to arXiv on August 26, 2024.

Traditionally, it is assumed that the pressure within a neutron star is isotropic; however, this study reveals that pressure is actually locally anisotropic. The researchers employed a two-fluid formalism to analyze the characteristics of neutron stars containing a subfraction of isotropic dark matter. They utilized three different equations of state (EOS): AP3, BSk22, and MPA1, which model various nuclear interactions.

Key properties of neutron stars, such as mass (M), radius (R), and dimensionless tidal deformability (Λ), were rigorously tested against observational data, including measurements from the binary neutron star merger GW170817 and NICER x-ray observations. The findings indicate that as the dark matter subfraction increases, higher anisotropies can still satisfy these observational constraints.

Moreover, the study found that increasing the coupling between dark matter and its mediator leads to the formation of a core-halo structure, where a dark matter halo surrounds the baryonic matter. Specifically, for coupling values of g = 10^{-4}, 10^{-3.7}, and 10^{-3.5}, the maximum radius (R_max) of the neutron star decreases with increasing anisotropy. This behavior contrasts with scenarios where there is no dark matter present.

The implications of this research are significant, as it suggests that binary pulsar systems could potentially provide constraints on the extent of dark matter-admixed anisotropic neutron stars, or even offer evidence for their existence. The full study can be accessed at arXiv:2408.14020.