In an effect known as Faraday rotation, a linearly polarized radio wave rotates in its position angle as it travels through a magnetized gas. This effect can be used to determine the strength of the intervening magnetic field. This project, led by Dr. Bryan Gaensler at Harvard University, pursues new observing and analysis techniques for studying faint background polarization, and for measuring the consequent Faraday rotation. The magnetic properties of interstellar gas can then be measured over wide regions of the sky, allowing one to map out both ordered and turbulent structures in otherwise invisible magnetic fields. These measurements will be applied to polarization data on both our own Milky Way and on the two nearest galaxies to our own, the Large and Small Magellanic Clouds. These data will be used to characterize the strength and scale of magnetic turbulence, both in diffuse interstellar gas and towards specific sources. How the properties of interstellar turbulence vary as a function of location, whether there is a transition from three- to two dimensional turbulence at a certain physical scale, and if turbulence is injected into the interstellar medium at particular sites, can all thus be determined. Using the fact that Faraday rotation in foreground sources can depolarize polarized background emission, one can also determine the gas density, magnetic field strength and degree of turbulence within discrete foreground objects. In this project, this phenomenon will be used to measure the scale of turbulent eddies in HII regions, to trace out the enhanced turbulence produced by supernova remnant shocks, and to probe the interaction between young stars and molecular clouds. Finally, polarization data will be used to determine the overall magnetic field structure of the Milky Way and of the Magellanic Clouds. Using the geometry of these fields and their relation to the distribution of interstellar gas, one can determine how galactic magnetism is generated. The overall goal of this project is to reach a full understanding of how magnetic fields are distributed throughout space, ranging from the small scales associated with random motions and turbulence, up to global Galactic structure. The fundamental contribution made by magnetic fields to the energetics and dynamics of our Galaxy and of every object within it are often overlooked - this project should amend this situation.
It is challenging for lay people of all ages to understand just what it means to measure the radio emission from space, and to comprehend the process through which these measurements are carried out. As a complement to the scientific program described above, activities will therefore be developed whose aim will be to make some of the astrophysical themes underlying this project accessible to middle- and high-school students. Specifically, activities will be designed which demonstrate that radio waves are a form of electromagnetic radiation, which explain how radio astronomers gather their data, which highlight the need to avoid and overcome radio frequency interference, and which explain the principles underlying interferometry. These activities will be piloted in local schools, assessed for their levels of student engagement and comprehension, refined and field-tested in a larger number of classrooms, and then made freely available via the WWW. ***
