Hypersonic beam driven by high-energy particles in extragalactic radio sources

A mechanism is proposed for the formation of collimated beams in radio galaxies. The collimated flows which are non-thermally driven by high energy particles and magneto-hydrodynamic (MHD) waves are presented. The galactic nucleus surrounded by a cool gas is investigated. The cool gas accretes onto the nucleus and the accretion matter can confine the wave zone around the nucleus in which the high energy particles are completely locked to the MHD waves. When a quasi-radial magnetic field is embedded in the accretion flow, the MHD wave packets are collimated into the direction of symmetry axis of the galactic nuclear disc. The fluid around the nucleus is considered to be accelerated and heated by the MHD waves and ejected along the axis.A complete set of hydrodynamic equations which contain the energy transfers of high energy particles and MHD waves is presented. One-dimensional flows which are in pressure equilibrium with the surrounding accretion matter are calculated. When the energy density of the MHD waves is higher than that of the thermal energy, the fluid flow is strongly collimated in a narrow beam. When the MHD waves are strongly damped by the resistivity of the fluid at the great distance from the galactic centre, the collimated beam broadly reexpands. On the basis of the collimated beams driven by high energy particles, the radio morphology of the double radio sources is discussed.