Helical magnetorotational instability in theory and experiment

The magnetorotational instability (MRI) is widely believed to play a key role in cosmic structure formation by maintaining turbulence and enabling angular momentum transport in accretion disks. The helical version of MRI (HMRI) was recently shown to have a scaling behaviour that is quite different to that of the standard version of MRI. Yet both types are continuously connected. We solve this apparent paradox by showing the emergence of an exceptional spectral point at which the slow magneto-Coriolis wave and one inertial wave coalesce and exchange their branches. Further, we compare the results of the PROMISE experiment on HMRI with various numerical predictions.