Measuring Magnetic Fields in Interstellar Gas, in the Milky Way, and Beyond

Gaensler Bryan, bryan.gaensler@sydney.edu.au, The University of Sydney, Australia

Abstract
Stars and planets form from the gravitational collapse of clouds of gas. Thus the seed fields for solar, stellar and planetary magnetism are the much weaker magnetic fields of the diffuse interstellar medium. I will describe the key techniques that astronomers have developed to map magnetism in interstellar gas, to study the magnetic field geometry of the Milky Way and other galaxies, and to constrain the overall large-scale magnetic field of the Universe. These studies reveal random and tangled morphologies of the magnetic field on small scales, but show that magnetic fields are surprisingly organized and coherent on large scales. I will conclude by describing innovative new studies of radio polarization and Faraday rotation that have allowed us to overcome some long-standing challenges in the field, and which have revealed stunning new views of the magnetic structure of astronomical turbulence, interstellar gas clouds and the overall Milky Way. These experiments pave the way to the opening of the full magnetic Universe with the next generation of radio telescopes, culminating in the Square Kilometre Array.