Do Magnetic Fields Destroy Black Hole Accretion Disk g-Modes?

TL;DR

This paper investigates whether magnetic fields can destroy g-modes in black hole accretion disks, finding that magnetic fields, especially radial components, do not necessarily eliminate these modes, supporting their potential role in explaining QPOs.

Contribution

The study extends previous theoretical work by analytically assessing magnetic field effects on g-modes, showing that magnetic fields do not necessarily suppress these oscillations.

Findings

Magnetic fields do not inherently destroy g-modes.

Radial magnetic field components can preserve g-modes.

Results align with recent simulation saturation values.

Abstract

Diskoseismology, the theoretical study of normal mode oscillations in geometrically thin, optically thick accretion disks, is a strong candidate to explain some QPOs in the power spectra of many black hole X-ray binary systems. The existence of g-modes, presumably the most robust and visible of the modes, depends on general relativistic gravitational trapping in the hottest part of the disk. As the existence of the required cavity in the presence of magnetic fields has been put into doubt by theoretical calculations, we will explore in greater generality what the inclusion of magnetic fields has to say on the existence of g-modes. We use an analytical perturbative approach on the equations of MHD to assess the impact of such effects. Our main conclusion is that there appears to be no compelling reason to discard g-modes. In particular, the inclusion of a non-zero {\it radial} component of the magnetic field enables a broader scenario for cavity non-destruction, especially taking into account recent simulations' saturation values for the magnetic field.