E. N. Parker's theorem on the magnetohydrodynamic heating of the solar corona.

What is it about?

The 1972 Parker magnetostatic theorem explains how the Sun’s fully ionized, magnetized, X-ray emitting corona is readily maintained at million-degree temperatures everywhere. As an excellent electrical fluid-conductor, the corona is driven by the electric motor, Lorentz force exerted by its magnetic field, with fluid motions acting as a dynamo generating changes in the electric current and magnetic field. On the small scales, no force equilibrium is possible because balancing the Lorentz force endlessly forces a ubiquitous irrepressible formation of infinitesimally thin current sheets that must dissipate into heat by the otherwise negligibly small, coronal electrical resistivity. The featured article constructs an insightful understanding of the theorem by explicitly relating the components of this universal astrophysical process to the topology of the magnetic field.

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Photo by Ryan Olson on Unsplash

Photo by Ryan Olson on Unsplash

Why is it important?

Modern space science began with the 1958 theoretical discovery of the late Eugene N. Parker (1927-2022) that the solar corona cannot be gravitationally bound but must perennially expand into the supersonic solar wind filling interplanetary space out to beyond the orbit of Pluto. This concept-transforming astrophysical reality was shortly confirmed by the early Soviet and US human made satellites. The investigation of outer space was a unique half-century venture, marked by NASA’s twin spacecraft Voyager I and II having by 2022 reached the transition of the wind into interstellar space, and by NASA’s current Parker Solar Probe (launched in 2018) orbiting into the Sun to detect the source of the wind. Parker had at the outset suggested that it is a ubiquitous magnetic heating that drives the coronal expansion into the wind, specifically identified by his 1972 theorem and intense investigations that followed. The constructive understanding of the theorem presented in the featured article paves way for research advancements on the spontaneous current sheets that today explain why stars and galaxies commonly possess X-ray coronae; see the images of the X-ray stellar coronae in the Carina constellation available at the URL below of the NASA Chandra X-ray Observatory. Further reading: Spontaneous current sheets in magnetic fields with applications to stellar X-rays, E. N. Parker, Oxford U Press, 1994. Conversations on electric and magnetic fields in the Cosmos, E. N. Parker, Princeton U Press, 2007. The Sun as a guide to stellar physics, edited by O. Engvold, J.-C. Vial & A. Skumanich, Elsevier, 2019.

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