![]() ![]() He reasoned that within the Sun’s magnetized plasma any bulk motions of electrically charged particles would disturb the magnetic field, creating waves that can carry huge amounts of energy along vast distances – from the Sun’s surface to its upper atmosphere. These fields are then dragged up from the Sun’s interior by convection, and burble onto its visible surface in the form of dark sunspots, which are clusters of magnetic fields that can form a variety of magnetic structures in the solar atmosphere. The movement of this plasma in the convection zone – the upper part of the solar interior – produces huge electrical currents and strong magnetic fields. The Sun is composed almost entirely of plasma, which is highly ionized gas that carries an electrical charge. Scientists looked to the Sun’s properties to explain this disparity. The extreme heat of the Sun’s corona is one of the most vexing problems in astrophysics. Edlén and Grotrian’s finding that the Sun’s corona is so much hotter than the photosphere – despite being further from the Sun’s core, its ultimate source of energy – has led to much head-scratching in the scientific community. Over many decades of study, the photosphere’s temperature has been consistently estimated at around 6,000☌. Estimating the photosphere’s heat has always been relatively straightforward: we just need to measure the light that reaches us from the Sun and compare it to spectrum models that predict the temperature of the light’s source. This represents temperatures up to 1,000 times hotter than the photosphere beneath it, which is the surface of the Sun that we can see from Earth. The coronal heating problem has been established since the late 1930s, when the Swedish spectroscopist Bengt Edlén and the German astrophysicist Walter Grotrian first observed phenomena in the Sun’s corona that could only be present if its temperature was a few million degrees celsius. Our recent study has finally achieved this, validating Alfvén’s 80-year-old theory and taking us a step closer to harnessing this high-energy phenomenon here on Earth. The theory had been tentatively accepted – but we still needed proof, in the form of empirical observation, that these waves existed.
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