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10/26/2017: SO/NOAO Joint Colloquium Series: Ethan Vishniac, JHU

Room: 

Title: Dynamos – How do they work?

Abstract:
The generation of large scale magnetic fields in stars and galaxies is a striking example of self-organization, the growth of large scale structure driven by small scale turbulence. The analytic theory describing this process is understood to contain problems and internal contradictions, as well as failing to generate testable predictions. In particular, the conservation of magnetic helicity gives rise to “alpha-suppression”, a process which turns off the dynamo before the large scale magnetic field reaches observed saturation strength. I will show how differential rotation and turbulence can drive a flux of magnetic helicity and explain how this process is the primary driver of the large scale magnetic field generation. Simple scaling laws derived from this picture explain the observed dependence of stellar magnetic fields on rotation and predict rapid field growth in young galaxies. I will also comment on some of the challenges in simulating dynamo processes numerically.

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