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Physics and Astronomy

Physics & Astronomy Colloquium

3:30 PM, Friday, September 19, 2008
Room 155, Chem-Phys Building

Dr. Gary Ferland
Department of Physics and Astronomy
University of Kentucky

Orion: Star formation in a magnetized medium
The Orion environment, its Nebula, molecular cloud, and star cluster, is the nearest region of active star formation. Young O stars ionize the surface of the molecular cloud, creating a layer of hot gas, the H II region. Observations of H I 21 cm Zeeman polarization measure the magnetic field within the part of the cloud that lies in front of the H II region. Analysis shows that magnetic pressure exceeds the turbulent or thermal gas pressures. I describe recent advances in numerical simulations of the ionization, chemistry, and thermal state of the molecular cloud and H II region. The picture that emerges is surprisingly simple. Radiation pressure pushes interstellar material away from the star cluster and compresses the ambient magnetic field until magnetic pressure is able to resist the starlight. The overall geometry is in approximate hydrostatic equilibrium. This overall simplicity has implications for very distant starburst galaxies where similar physics must occur but on a far grander scale.

Refreshments will be served in CP 155 at 3:15 PM