Probing astrophysical jet formation in the laboratory

Astronomers have observed collimated jets of material flowing outward from objects in outer space, but scientists have not pinpointed how these jets can become so incredibly long. Lavine and You reported an explanation for jet formation in astrophysical objects.

Previous reports suggested magnetic fields could confine plasma and cause astrophysical jets to form, but it was unclear how those jets could remain stable under such powerful magnetic forces. The paper presents the first experimental evidence of stable, magnetized jet formation and suggests the jet is the natural result of a plasma self-organizing into a relaxed double helical shape.

“The plasma jet is long and stable with strong helical shear flows, without any close-fitting walls, so the whole structure resembles two intertwined Archimedes screws rotating inside a plasma tube with the observer in the frame of the screws,” co-author Eric Lavine said.

To produce a stable jet, the authors built a triple electrode plasma gun designed to mimic a rotating accretion disk around a star or black hole. Then, they applied current to the apparatus, which in turn changed the structure of the applied magnetic field. The authors could observe how the magnetic field and the shape of the resulting jet evolved over time.

“These results support the hypothesis that self-organization and driven relaxation, theories borrowed from hydrodynamics of tornadoes and plasma dynamics of fusion concepts, could be a universal, intrinsic explanation for astrophysical jet formation, collimation, and stability,” Lavine said.

The authors are continuing to probe the mechanisms underlying the stable jet formation by developing theories and simulations.

Source: “Observations of a plectonemic configuration in a stable magnetized plasma jet,” by Eric Sander Lavine and Setthivoine You, Physics of Plasmas (2020). The article can be accessed at https://doi.org/10.1063/5.0044034 .