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This Week at Physics

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Events on Monday, March 11th, 2019

Plasma Physics (Physics/ECE/NE 922) Seminar
Numerical modeling of magnetic self-organization at the top of the solar convection zone
Time: 12:05 pm
Place: 2241 Chamberlin Hall
Speaker: John O'Bryan, University of Washington-Seattle
Abstract: Nonlinear, numerical computation with the NIMROD code is used to explore magnetic self-organization near the narrow, convectively unstable super-adiabatic layer at the top of the solar convection zone. The convective turbulence produced by the super-adiabatic rapidly saturates with kinetic and magnetic energy fluctuations in equipartition. Magnetic self-organization produces a radially-localized, latitudinally-elongated magnetic structure. The convective turbulence drive is stabilized by magnetic field, which limits the achievable magnetic field from localized turbulence alone. Differential rotation of the sun creates an inductive electric field which also causes growth of the magnetic field within the structure, the rate of which scales with its magnitude. The saturated small-scale turbulence can also drive a large-scale dynamo through the magnetic shear-current effect. When considered together, the localized convective turbulence and rotational flow shear create a robust mechanism for magnetic field generation, regardless of its magnitude. The nonlinear evolution of such a shallow magnetic structure may provide insight into the evolution of surface magnetic features.
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Astronomy Colloquium
Monday special talk
Decoding the Magnetic Universe
Time: 3:30 pm
Place: 4421 Sterling Hall, 3:30 PM Coffee and cookies, 3:45 PM Talk Begins
Speaker: Ann Mao , Max Planck Institute for Radioastronomy
Abstract: Dynamically important magnetic fields have been shown to play pivotal roles in processes that are closely linked to galaxy evolution, such as disk-halo interaction, gas accretion and galactic-scale outflows in local galaxies. However, how galaxies and their magnetic fields have co-evolved since the early Universe remains an unsolved fundamental question in astro-plasma physics and cosmology due to the lack of galactic magnetic field measurements beyond the local Universe.

In this talk, I will first describe how the advent of broadband radio polarimetry is revolutionizing the field of cosmic magnetism by enabling unambiguous and precise polarization measurements. Moreover, these broadband polarization data allow one to derive magnetized gas properties that were impossible to obtain in the past with narrowband data and these new data are now shedding new light on galactic magnetic fields near and far.

I will then demonstrate how broadband polarimetry, in combination with innovative observational methods can allow us to, for the first time, robustly measure magnetic fields in galaxies in previously uncharted redshift regimes. I will present the first results from our campaign, including our record-holder detection of coherent magnetic fields in a disk galaxy as seen 4.6 Gyrs ago, with similar field strength and geometry to local galaxies. This is the most distant galaxy to-date with a robust magnetic field measurement and it is consistent with mean-field dynamo generated fields already in place when the Universe was 2/3 of its current age. I will describe our efforts to interpret the observed magnetic fields in distant galaxies by producing synthetic polarimetric observations from dynamo theories and cosmological magneto-hydrodynamics simulations.

To conclude, I will discuss exciting prospects of decoding the origin and evolution of galactic magnetic fields with Square Kilometre Array pathfinders and the next generation radio telescopes.
Host: Professor Ellen Zweifel
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