In accretion disks with large-scale ordered magnetic fields , the magnetorotational instability ( MRI ) is marginally suppressed , so other processes may drive angular momentum transport leading to accretion .
Accretion could then be driven by large-scale magnetic fields via magnetic braking , and large-scale magnetic flux can build-up onto the black hole and within the disk leading to a magnetically-arrested disk ( MAD ) .
Such a MAD state is unstable to the magnetic Rayleigh-Taylor ( RT ) instability , which itself leads to vigorous turbulence and the emergence of low-density highly-magnetized bubbles .
This instability was studied in a thin ( ratio of half-height H to radius R , H / R \approx 0.1 ) MAD simulation , where it has a more dramatic effect on the dynamics of the disk than for thicker disks .
Large amounts of flux are pushed off the black hole into the disk , leading to temporary decreases in stress , then this flux is reprocessed as the stress increases again .
Throughout this process , we find that the dominant component of the stress is due to turbulent magnetic fields , despite the suppression of the axisymmetric MRI and the dominant presence of large-scale magnetic fields .
This suggests that the magnetic RT instability plays a significant role in driving angular momentum transport in MADs .