This material is not always the conventional jet in an early stage; Barthel has shown that radio galaxies of large projected size (i.e. presumably viewed 90° to the jet axes) can have superluminal motions, and proposed an intermediate model in which material is initially ejected over a broad cone angle. Only the tiny fraction coming near our line of sight is boosted enough to see at high angular resolution, and it is this fraction that would exhibit superluminal motion. On larger scales, structures in the M87 jet a kiloparsec from the core have been found to show transverse velocities of 0.3 - 0.5 c (Reid et al 1989 ApJ 336, 112; Biretta et al. 1989 ApJ 342, 128) - so far the only direct evidence that something in large-scale jets is moving at high speeds. In M87, HST imaging shows individual features with apparent transverse speeds anywhere from 0.6-6 c (Biretta et al. 1999 ApJ 520, 621). These make sense for γ~6 and a jet oriented within 19° to the line of sight, rather different than the visual impression shown in the image below (a
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This note was uploaded on 11/10/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.