A one-dimensional model of plasma flow from the accretion disk to the magnetic poles of a neutron star

Within the fluid dynamics framework, this study models the steady-state plasma flow from the accretion disk to the poles of a highly magnetized (≳1011 G) and slowly spinning (period ∼ 10 s) neutron star (NS) with aligned magnetic and rotational axes. We present a numerical study of the corresponding magnetized plasma flow. For our parameter space, numerical solutions reveal that the plasma density (ρ) increases ∼105−108 times toward the NS surface due to a narrowing cross section, from ∼10−7g/cm3 at the disk to 10 g/cm3 near the NS surface in the maximum compression case, with the plasma flow remaining subsonic. Plasma, unlike in previous studies, first slows down to a minimum due to opposing gravity, despite the compressing cross section of the funnel; then, it accelerates up to near the NS surface. The temperature (T) increases adiabatically from 106 K to ∼1011K, with the sound speed cs(∝T) being higher than the plasma flow velocity (v). Variations show that higher accretion rates (Ṁ≳5×1016g/s) boost density; stronger magnetic fields (1011–1013 G) lengthen the funnel, enhancing compression and acceleration. Initial Mach numbers (M0=0.1to0.9) yield denser flows for lower values. Since the adiabatic assumption is valid up to the point r ≳ 3.39 r0, plasma parameters near the NS surface are obtained by extrapolating their profiles beyond the validity region. The primary quantitative deliverable of the model is the plasma state at the upper accretion column. The presented results bridge the plasma parameters at the magnetospheric boundary to the accretion columns via magnetospheric funnel flow, concluding with the plasma parameters near the NS surface in the mid-region to upper region of the accretion column.