In astronomical phenomena such as neutron stars, the strength of the magnetic field can be extremely large, approaching the quantum Schwinger field (4.4 x 10¹³ Gauss). At these strengths, pair production can occur leading to a plasma dominated by electron-positron pairs. It is inevitable that magnetic reconnection occurs at some points in the magnetosphere. In the context of this reconnection, multiple flux-tubes referred to as magnetic islands can be found. Compression of the fields of a magnetic island leads to enhanced radiative cooling, and in turn further compression. The resulting runaway process leads to quantum electrodynamic (QED) effects such as pair production.

We have performed a 3D ab initio PIC simulation of magnetic reconnection, starting from a Harris equilibrium pair plasma, where most of the energy is in the form of magnetic fields, which takes into account hard photon emission and pair production at the rates predicted from QED. The video shows the development of reconnection, the formation of magnetic islands separated by reconnection sites, and the compression of a magnetic island generated due to reconnection. The magnetic field lines are colored by magnitude from weakest (blue) to strongest (orange). The regions where the field is compressed to more than 125% of the initial strength, located at the centers of the magnetic islands, are highlighted in green. An x-point located between two prominent magnetic islands is identified along with the direction of the plasma outflows which drag magnetic flux into the islands. The projected field strength displayed behind in blue, from weakest (black) to strongest (white). This further highlights the regions where the strongest magnetic fields occur, and thus where we expect QED effects such as hard photon emission and pair production to play an important role.

For more information, see K. M. Schoeffler, T. Grismayer, D. Uzdensky, R. A. Fonseca, and L. O. Silva, Bright Gamma-Ray Flares Powered by Magnetic Reconnection in QED-strength Magnetic Fields, The Astrophysical Journal 870 (1), 49 (2019), available here.