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D. L. Meier (Jet Propulsion Laboratory)
For some time, direct very long baseline interferometry imaging observations have shown that collimated, relativistic flow at speeds up to a Lorentz factor of 10 (0.995c) are possible in active galactic nuclei. Such jet flows already are difficult to achieve theoretically, and usually require the relativistic environment of a supermassive black hole. The problem has been made more challenging by recent observations of such disparate objects as intra-day variable (IDV) radio blazars and gamma-ray burst sources, which indicate possible jets with Lorentz factors as high as perhaps 100.
Recently, several groups around the world have begun to test theories of jet formation using magnetohydrodynamic (MHD) simulations (computer simulations of magnetized gas flow around black holes). While it is now generally accepted that jets, including relativistic ones, are accelerated and collimated by magnetized accretion disks, the Lorentz factors that have been achieved in these simulations still do not approach those suggested by IDVs or gamma-ray burst sources. In this talk I will review the field of simulations of MHD jet formation, with an emphasis on producing highly relativistic outflows and the role that black hole angular momentum might play. I will also present some recent general relativistic simulations of magnetized accretion onto rotating black holes that illustrate some of these points.
Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to the National Aeronautics and Space Administration.