The kinematic Kelvin–Helmholtz instability-driven dynamo: implications for merging compact objects
Density roll-up in a Kelvin–Helmholtz billow at Re = 8192 and 140 shear times. Detail from Figure 3a, Beattie et al. (2026).A rapid dynamo between merging stars
When two neutron stars meet, their shear layer rolls into Kelvin–Helmholtz billows. How do these motions build the intense magnetic fields found in merger simulations?
We follow three stages: shear winds the initial field; secondary instabilities break the billows into three-dimensional motions; and a dynamo amplifies both the fluctuating field and a mean field perpendicular to the original flow plane. At high Reynolds number, the dynamo growth rates become independent of Reynolds number.
Applied to neutron-star mergers, our models predict rapid vertical-field seeding and magnetar-strength fields as the dynamo leaves its kinematic stage on roughly 0.1 ms timescales. This suggests that global simulations may not resolve the relevant amplification regime.
