Engineering topics
Publications and source records attributed to Meier, D..
Fully relativistic and causal equations for the flow of charge in curved spacetime are derived. It is believed that this is the first set of equations to be published that correctly describes the flow of charge, as well as the evolution of the electromagnetic field, in highly dynamical relativistic environments on timescales much shorter than the collapse time (GM/c3).
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We are using the VSOP mission to observe a complete sample of Pearson-Readhead survey sources at 4.8 GHz to determine core brightness temperatures and pc-scale jet properties.
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The physical conditions in the inner parsec of accretion disks believed to orbit the central black holes in active galactic nuclei can be probed by imaging the absorption of background radio emission by ionized gas in the disk.
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We present a map of the J=2-1 transition of (sup 13)CO in the starburst nucleus of IC 342 made with the Owens Valley Millimeter Array.
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The structure of AGN accretion disks on sub-parsec scales can be probed through free-free absorption of synchrotron emission from the base of symmetric radio jets.
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The Einstein ring gravitational lens PKS 1830-211 consistents of two bright, milliarcsecond-scale radio components separated by 1 arcsec and connected by a fainter ring of radio emission (Rao and Subrahmanyan 1988; Jauncey et al. 1991).
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Understanding how astrophysical jets are formed is important for understanding the nature and evolution of such phenomena as active galactic nuclei and quasars, Galactic superluminal x-ray sources, and young stellar objects.
A model is described in which radio jet formation in accreting objects is suppressed by processes which occur when the accretion rate approaches the Eddington limit. This was motivated by GRO J1655-40 and other objects which show an anticorrelation between high luminosity and the onset of a radio jet. The jet production mechanism employed is the Blandford-Payne MHD acceleration process, seeded by an e'e- pair wind. Observations indicate that all key ingredients of this mechanism are, or should be, present in these sources. Observed jet velocities and total powers are consistent with theoretical and numerical predictions of this model. The primary jet suppression mechanism proposed is the Papaloizou-Pringle compressible shear instability, which should disrupt the jet-producing region of the disk when the accretion rate approaches about one-third Eddington. The turn-on of the jet in GRO J 1 655 - 40 is consistent with this estimate. When super-Eddington, the disk should also drive an optically thick, subrelativistic wind, which may be a secondary jet suppression mechanism. The possible presence of such a wind is seen in the early spectral evolution of GRO J1655-40 and in the broad absorption lines of certain quasi-stellar objects (QSOs). Important tests of the model would be independent measurements of the compact object masses in these sources, a comparison of normal and broad absorption line (BAL) QSO X-ray spectra to see if the latter objects are significantly cooler, and a low-frequency search around BAL QSOs to see if at least some have fossil radio sources.
We have used massively parallel supercomputer simulations to perform an extensive study of a plausible mechanism for producing the jets seen in extragalactic radio sources - acceleration and collimation by coronal magnetic fields in an accretion disk orbiting a central black hole. We find that such disks can propel jets for a wide range of coronal conditions. The terminal jet velocity is a strong function of the magnetic field equatorial component. Acceleration and collimation are produced by a tight azimuthal field coil generated in the corona, rather than by a stiff poloidal field extending to large distances. The jets are pressure-confined when the external medium pressure is high, but magnetically- confined when it is low.