Theory of the M87 jet

We summarize theoretical ideas on the dynamical properties of the jet in M 87 and its relationship to the inner lobe and adjacent emission line filaments. Shocks in one form or another and the Kelvin Helmholtz instability have long been held to be related to the emission from the M 87 jet and its shape respectively. We give a brief account of recent work which attempts to relate these two pieces of physics. We note that it is important to take relativistic effects on the appearance of shocks into account when attempting to determine the intrinsic obliquity of shocks. Our model naturally leads to consideration of the interaction of the jetdriven expanding inner lobes with surrounding dense gas. We have suggested that radiative shocks driven into clouds (no. density ∼ 1 − 10 cm−3) are responsible for line emission from this gas. Outstanding problems are the confinement of the M 87 jet in the inner 100 pc and its initial approximately linear expansion.