New insights into how luminous jets form around rapidly-rotating black holes have been provided by advanced computer simulations done by astrophysicists in the US and France. Their model could play an important role in interpreting future electromagnetic and gravitational-wave observations of black holes.
Black hole jets are some of the brightest sources of X-ray and radio emissions known to astronomers. These jets are formed when black hole surfaces spinning at relativistic speeds are threaded with magnetic field lines. Interactions with infalling gas cause these fields to become tightly wound into helixes around the black hole’s axis of rotation. Huge amounts of energy within the coiled field lines is dissipated gradually through the creation of electron-positron pairs. A cascade process creates a huge jet of energetic plasma that emits vast amounts of electromagnetic radiation.
Much of the jet-formation process remains a mystery, however, and astrophysicists are trying to improve their knowledge using general relativistic magnetohydrodynamics (GRMHD) computer simulations. Despite successes in recreating energy transfer between black holes and magnetic fields, these simulations face a major shortcoming. Rather than regarding the plasma formed by pair-creation as a collection of individual particles, GRMHD treats it as a continuous fluid. Such a crude approximation means that small-scale variations in plasma density; important for accurately modelling its overall dynamics, are disregarded.
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