Effects of Magnetic Fields on the Diskoseismic Modes of Accreting Black Holes

TL;DR

This paper investigates how magnetic fields influence diskoseismic oscillation modes in accreting black holes, revealing that magnetic fields can suppress certain modes while allowing others to persist, impacting interpretations of observed X-ray variabilities.

Contribution

It demonstrates that even weak magnetic fields can significantly alter or eliminate specific disk oscillation modes, challenging previous models that ignored magnetic effects.

Findings

Weak magnetic fields can destroy g-mode trapping zones.

C-modes are strongly affected by poloidal magnetic fields.

p-modes remain largely unaffected by magnetic fields.

Abstract

The origin of the rapid quasi-periodic variabilities observed in a number of accreting black hole X-ray binaries is not understood. It has been suggested that these variabilities are associated with diskoseismic oscillation modes of the black hole accretion disk. In particular, in a disk with no magnetic field, the so-called g-modes (inertial oscillations) can be self-trapped at the inner region of the disk due to general relativistic effects. Real accretion disks, however, are expected to be turbulent and contain appreciable magnetic fields. We show in this paper that even a weak magnetic field (with the magnetic energy much less than the thermal energy) can modify or "destroy" the self-trapping zone of disk g-modes, rendering their existence questionable in realistic black hole accretion disks. The so-called corrugation modes (c-modes) are also strongly affected when the poloidal field approaches equal-partition. On the other hand, acoustic oscillations (p-modes), which do not have vertical structure, are not affected qualitatively by the magnetic field, and therefore may survive in a turbulent, magnetic disk.