Scientists from Princeton Plasma Physics Laboratory (PPPL) of the Department of Energy’s (DOE) in the U.S. have discovered essential conditions that give rise to fast magnetic reconnection, the process that triggers solar flares, auroras, and geomagnetic storms that can disrupt signal transmissions and other electrical activities, including cellphone service.
The process occurs when the magnetic field lines in plasma, the hot, charged state of matter composed of free electrons and atomic nuclei, break apart and violently reconnect, releasing vast amounts of energy. This happens in thin sheets of plasma, called current sheets, in which electric current is strongly concentrated.
The findings add to an earlier theory of fast reconnection developed mathematically by incorporating computer simulations. The new results include a predictive model that gives a complete description of the physics involved.
Scientists from PPPL states, the impact of reconnection can be felt throughout the universe. The process may cause enormous bursts of gamma-ray radiation thought to be associated with supernova explosions and the formation of ultra-dense neutron stars and black holes.
PPPL physicist Yi-Min Huang, lead author of a paper reporting the findings in Astrophysical Journal, said, “A gamma-ray burst in our Milky Way galaxy if pointing towards Earth, could potentially cause a mass extinction event.” Huang added, “Clearly, it is important to know when, how, and why magnetic reconnection takes place.”
After an extended period of quiescent behavior by magnetic fields inside current sheets, scientists have observed that reconnection happens suddenly. Using computer simulations and theoretical analysis, the physicists demonstrated that a phenomenon called the “plasmoid instability” creates bubbles within plasma that can lead to reconnection.
This happens when the plasma must have a high Lundquist number, which characterizes how well it conducts electricity; and random fluctuations in the magnetic field of the plasma provide “seeds” from which the plasma instability grows.
These conditions allow plasmoid instabilities to give rise to reconnection in current sheets. “Our study suggests that disruption of the current sheet caused by the plasmoid instability may provide a trigger,” Huang said.