A novel jet model: magnetically collimated, radiation-pressure driven jet

Relativistic jets from compact objects are ubiquitous phenomena in the Unvierse, but their driving mechanism has been an enigmatic issue over many decades. Two basic models have been extensively discussed: magnetohydrodynamic (MHD) jets and radiation-hydrodynamic (RHD) jets. Currently, the former is more widely accepted, since magnetic field is expected to provide both the acceleration and collimation mechanisms, whereas radiation field cannot collimate outflow. Here, we propose a new type of jets, radiation-magnetohydrodynamic (RMHD) jets, based on our global RMHD simulation of luminous accretion flow onto a black hole shining above the Eddington luminosity. The RMHD jet can be accelerated up to the relativistic speed by the radiation-pressure force and is collimated by the Lorentz force of a magnetic tower, inflated magnetic structure made by toroidal magnetic field lines accumulated around the black hole, though radiation energy greatly dominates over magnetic energy. This magnetic tower is collimated by a geometrically thick accretion flow supported by radiation-pressure force. This type of jet may explain relativistic jets from Galactic microquasars, appearing at high luminosities.