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