2026

March 6: Large-scale dynamos driven by shear-flow-induced jets

Speaker: Bindesh Tripathi (Columbia University)

Abstract: The origin of cosmic magnetic fields remains an open problem in astrophysics.  In 1955, Eugene Parker proposed a mean-field dynamo theory by parameterizing the effects of small-scale turbulence.  Although this framework successfully reproduces observed large-scale magnetic fields, it relies on parameters that are difficult to constrain from first principles.  Here, by analyzing an unstable, driven shear flow, we develop analytic theory and perform three-dimensional simulations of turbulence with up to 4,096 × 4,096 × 8,192 grid points.  The simulations demonstrate ab initio generation of quasi-periodic, large-scale magnetic fields.  The generation operates via the mean-vorticity effect—an additional mean-field dynamo process postulated in 1990—and is driven by robust, large-scale, three-dimensional, nonlinear jets.  Predictions from the jet-driven dynamo are confirmed using data from a shear-driven laboratory dynamo experiment.  This dynamo mechanism applies to a variety of astrophysical systems, including binary neutron star mergers, where it can produce some of the strongest magnetic fields in the Universe, providing signals for multi-messenger astronomy.


March 6: Modelling Magnetic Dissipation in Magnetized Magnetospheres

Speaker: Michael Grehan (University of Toronto)

Abstract: Highly magnetized neutron star and black hole magnetospheres can convert magnetic energy into high-energy emission through shocks and reconnection. In this talk, I present recent relativistic MHD simulations of two such processes. First, I discuss “monster shocks” — ultra-relativistic magnetized shocks that form when waves launched from a neutron star steepen in a magnetically dominated magnetosphere. Our simulations confirm analytical predictions for equatorial shocks, extend them to oblique geometries, and show that additional magnetospheric modes can fragment the shock front, reduce magnetization, and intermittently generate secondary shocks. Second, I present a kinetic-motivated effective resistivity for relativistic resistive MHD that links the reconnection electric field to charge-starved current densities. This approach reproduces the reconnection rates seen in kinetic models, both in local current sheets and global black hole magnetospheres, and has direct applications to pulsar simulations.

February 20:  Tidal Disruption of a Magnetized Star by an Intermediate-Mass Black Hole

Speaker: Omer Bromberg  (Tel Aviv University)

Abstract: TBA