|
Physical Society Colloquium
Matthew Lister National Radio Astronomy Observatory Very Long Baseline Interferometric (VLBI) techniques currently provide the highest angular resolution of any astronomical imaging technique, and have provided the only direct evidence for relativistic outflows from the vicinity of supermassive black holes in active galactic nuclei (AGN). With the launch of the Japanese radio astronomy satellite HALCA in 1997, interferometric baselines have been extended to several Earth radii, such that the physics of extremely compact radio sources in the distant Universe can now be routinely investigated. I discuss recent space- and ground-VLBI observations of 32 of the brightest, most compact AGN in the northern sky. This work represents the highest angular-resolution survey in the history of astronomy, with an imaging resolution equivalent to the size of an astronaut's footprint on the Moon as seen from Earth. The inner structure of these AGNs generally consists of a yet-unresolved synchrotron-emitting `core' located at the base of a collimated jet outflow that is pointed nearly directly at us. I discuss current physical models for these jets, including evidence for helical streaming motions and oblique shocks in the flow, and describe how their appearance is heavily influenced by special-relativistic beaming and foreshortening effects.
Tuesday, February 5th 2002, 11:00 |