Physical explanation of the inverted magnetic–accretion deformation behavior

Investigate and explain why, for accreting magnetized neutron stars with total accretion rates below the threshold accretion rate \(\dot{M}_{th}\), increasing the poloidal magnetic-field strength can produce prolate spheroids while increasing the accretion asymmetry produces oblate spheroids, contrary to the behavior expected above \(\dot{M}_{th}\).

Background

The model predicts that magnetic stresses and thermally induced deformations from asymmetric accretion generally compete, with the relative sign of their contributions changing at a threshold accretion rate $\dot{M}_{th}$. Above this threshold, the poloidal magnetic field produces oblate deformations and asymmetric accretion produces prolate deformations. Below the threshold, the authors find an apparently inverted behavior: stronger magnetic fields produce prolate configurations, whereas greater accretion asymmetry produces oblate configurations.

The paper suggests that this inversion may result from the indirect influence of the magnetic field on temperature perturbations becoming more important than the direct Lorentz-force contribution, particularly because thermal perturbations can dominate the deformation. However, the authors explicitly state that they do not have a simple and convincing interpretation of the phenomenon, leaving its physical origin unresolved.