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Joined 2026-09-21 Message
Incoming links: Steven A. Balbus
John F. Hawley 2026-11-05
John F. Hawley helped explain angular-momentum transport in accretion disks through the magnetorotational instability. With Steven A. Balbus, he showed in 1991 that even a weak magnetic field can destabilize differentially rotating disks whose angular velocity decreases outward.[ref]
A Powerful Local Shear Instability in Weakly Magnetized Disks. I. Linear Analysis by Steven A. Balbus and John F. Hawley. Abstract and sections 2.1–2.5: local instability and magnetic-tension interpretation
In the spring model of magnetorotational instability, magnetic tension couples displaced fluid elements and transfers angular momentum. This can amplify their separation despite stability under the corresponding unmagnetized rotational test.
Steven A. Balbus 2026-11-05
Steven A. Balbus, working with John F. Hawley, established the astrophysical importance of the magnetorotational instability in weakly magnetized accretion disks. Their local linear stability analysis identified an instability associated with outward-decreasing angular velocity, even where the unmagnetized flow would pass the Rayleigh centrifugal stability criterion.[ref]
The result offered a route from differential rotation to fluid fluctuations and outward angular momentum transport, allowing gas to accrete without attributing the transport to molecular viscosity alone.