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Session 94 - Pierce Prize Lecture.
Invited session, Friday, January 09
International Ballroom Center,

[94.01] Fields of Dreams

A. A. Goodman (Harvard University)

Magnetic fields in the interstellar medium are critical to its structure and evolution, yet we have only the vaguest idea of their nature. Recent technological improvements, especially in the sensitivity of infrared and radio telescopes, have brought the density and velocity structure of the ISM into sharp focus, but our picture of how the field threads its way through the structures revealed remains a blur.

Theoretical models along with scant polarimetric and Zeeman data strongly suggest a key role for the magnetic field in many regimes, including star-forming regions, H I ``supershells," and the Galactic Center. In star-forming regions, both interstellar and protostellar fields are expected to play a critical role: supporting clouds against rapid gravitational collapse; determining the nature of outflows from young stars; molding H II regions; and generally mitigating the turbulence which pervades these regions. The lack of detailed field maps--which should include both strength and structure measurements--severely restricts our attempts to understand the exact physical nature of magnetohydrodynamic interactions in the ISM.

This talk will summarize the existing evidence for a ``starring" role for the field in so many regions, and will then focus on the observational techniques available for mapping out the three-dimensional magnetic field. The techniques to be discussed include polarimetry of background starlight, polarimetry of thermal dust emission, and radio-frequency Zeeman observations. I will conclude with a ``dream" plan for how make the most progress in mapping out interstellar magnetic fields over the next ten years.

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