Séminaire IPAG

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Cosmic Magnetism and Plasma Microphysics

jeudi 16 juin 2022 - 11h00

Matthew Kunz - Princeton / IPAG
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The Universe is magnetized. While magnetic-field strengths of just ~10^{-18} G are required to achieve this both in our Galaxy and in clusters of galaxies, observations of Faraday rotation, Zeeman splitting, and synchrotron emission all make the case of ubiquitous ~μG fields. That these systems are not content with hosting weaker fields is surprising, at least until one realizes that the energy density of a ~μG field is comparable to that of the observed turbulent motions. It is then natural to attribute the amplification and sustenance of (at least the random component of) the interstellar and intracluster magnetic fields to the fluctuation (or "turbulent") dynamo. In this talk, we will explore the various ways in which plasma microphysics makes magnetic-field amplification in weakly collisional plasmas by macroscale turbulent motions both possible and efficient, with application to the intracluster medium of galaxy clusters. The predictions of this work are consistent with (i) deep Chandra X-ray observations of turbulence in the Coma cluster that suggest an anomalously low viscosity, (ii) recent LOFAR observations of diffuse radio emission in massive clusters when the Universe was only half of its present age, (iii) Faraday rotation maps of intracluster magnetic fields revealing structure on scales ~1-10 kpc, and (iv) plasma kinetics measured directly by in situ spacecraft in the solar wind. Time permitting (as a bonus), I will advertise theory and simulation demonstrating how resistive tearing changes the geometry of turbulently amplified magnetic fields at large magnetic Reynolds numbers.

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Hôtes : Benoît Cerutti & Geoffroy Lesur

Salle Manuel Forestini, 414 rue de la piscine, 38400 Saint Martin d'Hères