Physics of the M87 Jet
Motivated by the recent determination of proper motions of knots in the M87 jet by Biretta, Zhou, & Owen (1995), we have investigated the relationship between the dynamics of the jet and the kpc-scale radio and optical structure. We interpret the knots as internal shocks in the jet, and find that relativistic effects play an important role in their appearance. In particular, knot A, which appears to be almost transverse to the flow and seems to be viewed nearly edge-on, is in fact a highly oblique shock. The direction of its normal with respect to the flow lies within about 10° of the Mach angle, i.e., the angle of obliquity beyond which no shock is possible. In a frame comoving with the shock front, the incident streamlines make an angle of about 40° – 60° with respect to the shock normal. Knot A has a proper motion corresponding to only 0.51c, and the relativistic effects are modest. Its edge-on appearance is largely fortuitous. We have found, however, that relativistic effects would create a strong bias for shocks with apparent superluminal speeds to appear nearly edge-on.
KeywordsShock Front Proper Motion Lorentz Factor Oblique Shock Synchrotron Emissivity
- Bicknell, G. V., & Begelman, M. C. 1995, ApJ, submittedGoogle Scholar