Magnetic fields permeate the space between objects throughout the universe, from galaxy clusters to protogalaxies to nebulae like the one shown in figure 1. It’s not difficult to explain how those fields might be initiated: Weak fields originate in astrophysical plasmas through various mechanisms—for example, temperature or density gradients in the plasma that alter electron trajectories.

But it remains challenging to demonstrate how seed fields of 10−21 gauss in intergalactic space grow to their measured astronomical values of several microgauss. Theory suggests that turbulent motion in an astrophysical plasma amplifies tiny magnetic fields by converting kinetic energy into magnetic energy. Such a self-sustaining energy conversion mechanism is called a dynamo.

Dynamos are often distinguished between large scale and small scale. The familiar large-scale geodynamo relies on Earth’s symmetry-breaking rotation to generate a magnetic field that grows at scales larger than those of the liquid-core motion. But in a...

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