Compared to its interior, the surface of our sun is a cool 6,000 degrees Celsius. But beyond the surface, the sun’s corona heats up dramatically through interactions between plasma and strong magnetic fields. The exact mechanisms of this interaction have been mostly theoretical thus far, but a recent laboratory experiment has validated a part of that theory.
One explanation for coronal heating posits that the strong magnetic fields can accelerate magnetohydrodynamic waves called Alfvén waves to speeds faster than sound, and that at this crossover point, changes occur in the waves’ behavior. Using liquid rubidium, researchers were able to observe this crossover under laboratory conditions, confirming that the Alfvén waves change at the speed of sound in exactly the manner predicted by theory. (Image credit: NASA SDO; research credit: F. Stefani et al.; via Physics World)