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J. A. Biretta, E. S. Perlman, W. B. Sparks, F. D. Macchetto (STScI)
We present highlights from our four-year monitoring campaign on the M87 jet using the FOC and WFPC2 cameras on-board HST. Numerous optical features within the first arcseconds of the jet display apparent superluminal motion at speeds of 4c - 6c. These speeds indicate bulk flow with a Lorentz factor of 6 or greater, and strongly support unified models for this FR-I radio source. These speeds also constrain the velocity vector to be oriented within 19 degrees of the line of sight, indicating either the jet is misaligned with the circumnuclear gas disk, or that jet material moves on some helical path about the jet axis. The spectral evolution of the superluminal components will be discussed as well. These observations show internal jet structure in unprecedented detail, and reveal axissymmetric features extending to depths very near the jet axis, suggesting a layered structure within the jet.