3D MHD Simulations of Accretion onto Stars with Tilted Magnetic and Rotational Axes

M. M. Romanova, A. V. Koldoba, G. V. Ustyugova, A. A. Blinova, D. Lai, R. V. E. Lovelace

We present results of global three-dimensional (3D) magnetohydrodynamic (MHD) simulations of the accretion onto a magnetized star where both the magnetic and rotational axes of the star are tilted about the rotational axis of the disc. We observed that initially, the inner parts of the disc are warped due to the magnetic interaction between the external regions of the magnetosphere and the inner disc. Subsequently, larger parts of the disc become tilted and precess about the rotational axis of the star. After a few precessional periods, the disc becomes almost aligned with the equatorial plane of the star. This alignment may result from the winding of the magnetic field lines about the rotational axis of the star and the formation of a new magnetic configuration, where the magnetic pressure force acts to align the disc. Another possible explanation of this alignment is the magnetic Bardeen-Petterson effect where a part of the disc, precessing about the rotational axis of the star, settles in the equatorial plane due to the precessional and viscous torques in the disc.

https://arxiv.org/abs/2012.10826