A New Theory of Fast Magnetic Reconnection in Strongly Magnetized Plasmas

Fast magnetic reconnection may play a crucial role in particle acceleration within highly magnetized astrophysical environments such as black hole jets and pulsar winds. While Particle-in-Cell (PIC) simulations have observed a rapid reconnection rate in relativistic pair plasma reconnection, the underlying physical mechanism responsible for this rate has remained elusive. We present recent theoretical progress on the relativistic reconnection rate problem. In the case of antiparallel magnetic fields, we analytically show that the fast rate is controlled by the competition between thermal energy and bulk flow energy of the current carriers. In the relativistic regime, the requirement to sustain extreme current density prevents the build-up of plasma pressure at the x-line, creating a pressure void which pulls in the surrounding magnetic field lines. The newly bent field-lines produce an open outflow geometry, enabling a fast reconnection rate. We will also discuss ongoing efforts in understanding the guide field case. These results provide an important foundation for understanding how magnetic reconnection can explain observations of non-thermal spectra and high-energy transient flares around the most extreme objects in the universe.