Magnetic collimation of the relativistic jet in M87

The slow collimation of the relativistic jet of M87 which collimates from a wide opening angle of about 60 degrees at sub parscec scales to a smaller angle of about 10 degrees at the pc scale is modelled by means of a two-component MHD outflow consisting of a relativistic wind-type outflow from a central source and a non relativistic wind from a Surrounding disk. We employ a numerical code for the direct numerical solution of the steady state problem in the zone of super first magnetized flow and show that in this two-component model it is possible to easily collimate into a cylindrical jet all the mass and magnetic fluxes which are available from the central source. This magnetic collimation occurs over the scales suggested by observations of the M87 jet after the jet undergoes several oscillations in its width, as also found by earlier analytical solutions. A layer of increased density Surrounds the collimated jet, a result consistent with an emissivity which is observed to be much higher in a thin boundary layer than elsewhere in the jet.