Abstract: The origin of magnetic fields in the universe is of fundamental importance in view of their essential role in many astronomical phenomena, including star formation. Astrophysical magnetic fields owe their strength to dynamo action, but dynamos only amplify fields--they cannot create them. Magnetic fields could have originated early in the universe due to quantum processes, but these are uncertain. If these processes are inadequate, magnetic fields would have been produced by curved shocks after recombination by the Biermann battery process. However they are created, magnetic fields can be amplified by many orders of magnitude by a turbulent dynamo. Accurately simulating a turbulent dynamo as it amplifies the field from its initial value to equipartition is not currently possible since the numerical viscosity is several orders of magnitude larger than the actual one. As a result, MHD simulations of the formation of the first stars begin with an artificially large magnetic field. Most such simulations find that magnetic fields suppress the formation of low-mass stars, consistent with the absence of observed stars with no heavy elements.
Biography: Professor Christopher McKee received his AB degree from Harvard and his PhD in physics from UC Berkeley (1970). After a brief stay at Lawrence Livermore National Laboratory, he spent a year as a postdoctoral fellow at Caltech. He then went to Harvard as an assistant professor of astronomy for three years, and in 1974 he joined the Physics and Astronomy Departments at UC Berkeley. Since 2012 he has been an Emeritus Professor of Physics and of Astronomy. He has carried out theoretical investigations of a wide variety of astrophysical phenomena, ranging from the interstellar medium of the Galaxy to quasars and cosmic gamma-ray bursts. His current research focuses on the formation of stars. He has received a number of honors for his work: He is a member of the National Academy of Sciences, a fellow of the American Academy of Arts and Sciences, of the American Association for the Advancement of Science, of the American Physical Society, and a Legacy Fellow of the American Astronomical Society; he was the 2016 Russell Lecturer of the American Astronomical Society. With Joseph Taylor, he co-chaired the decadal survey in astronomy and astrophysics in 2000, which recommended what is now called the James Webb Space Telescope as its top priority. At UC Berkeley, he served as founding Director of the Theoretical Astrophysics Center, the Director of the Space Sciences Laboratory, the Chair of the Physics Department, the Interim Dean of Mathematical and Physical Sciences, and the Interim Vice Chancellor for Research.