Effects of asymmetric dark matter on a magnetized neutron star: A two-fluid approach

We study the interaction between dark matter (DM) and highly magnetized neutron stars (NSs), focusing on how DM particle mass, mass fraction, and magnetic field (MF) strength affect NS structure and stability. We consider self-interacting, nonannihilating, asymmetric fermionic DM that couples to NSs only through gravitational interaction. Using the Quantum Monte Carlo Relativistic Mean Field (QMC-RMF4) model with density-dependent magnetic fields, we investigate the magnetized equation of state and examine the accumulation of DM under various conditions. Our results show that as the DM fraction increases, the maximum gravitational mass of the NS decreases, especially for heavier DM particles, while lighter DM particles can induce a transition from a dark core to a halo structure, increasing the maximum mass. Strong MFs soften the equation of state and reduce the dark mass a NS core can retain before transitioning to a halo. By comparing our results with observations from Neutro Star Interior Composition Explorer and GW170817, we identify the possible range of DM parameters for these objects. We find that the magnetic field slightly changes these limits, mainly affecting the maximum NS mass and tidal deformability. These findings provide key insights into how DM and MF jointly shape the mass-radius relation and the stability of DM-admixed magnetized NSs.