Boundary layer on the surface of a neutron star

TL;DR

This paper models the gas flow near a neutron star's surface using hydrodynamical simulations, revealing different behaviors depending on the star's mass, temperature, and rotation, especially under radiation pressure dominance.

Contribution

It provides the first two-dimensional hydrodynamical models of accretion onto neutron stars considering both non-rotating and rotating cases with realistic parameters.

Findings

Gas pressure dominated case shows different flow patterns.

Realistic neutron star mass and temperature lead to radiation pressure effects.

Stationary solutions likely require the star to rotate rapidly.

Abstract

In an attempt to model the accretion onto a neutron star in low-mass X-ray binaries, we present two-dimensional hydrodynamical models of the gas flow in close vicinity of the stellar surface. First we consider a gas pressure dominated case, assuming that the star is non-rotating. For the stellar mass we take $M_{\rm star}=1.4 \times 10^{-2} \msun$ and for the gas temperature $T=5 \times 10^6$ K. Our results are qualitatively different in the case of a realistic neutron star mass and a realistic gas temperature of $T\simeq 10^8$ K, when the radiation pressure dominates. We show that to get the stationary solution in a latter case, the star most probably has to rotate with the considerable velocity.