The direct discovery of Alfvén waves in the solar photosphere is an important step towards exploiting their high energy potential here on Earth. This instrument has allowed us to make far more detailed observations and measurements of the Sun.Ĭombined with good viewing conditions, advanced computer simulations, and the efforts of an international team of scientists from seven research institutions, we used the IBIS to finally confirm, for the first time, the existence of Alfvén waves in solar magnetic flux tubes. One such instrument is the Interferometric Bidimensional Spectropolarimeter ( IBIS) for imaging spectroscopy, installed at the Dunn Solar Telescope in the U.S. There’s so much happening on the Sun’s surface and in its atmosphere – from phenomena many times larger than Earth to small changes below the resolution of our instrumentation – that direct observational evidence of Alfvén waves in the photosphere has not been achieved before.īut recent advances in instrumentation have opened a new window through which we can examine solar physics. Observing Alfvén wavesīut there remained the problem of actually observing these waves. These magnetic plasma waves are now called Alfvén waves, and their part in explaining coronal heating led to Alfvén being awarded the Nobel Prize in Physics in 1970. This diagram shows multiple layers, including the sun’s atmosphere. The heat travels along what are called solar magnetic flux tubes before bursting into the corona, producing its high temperature.īeneath the sun’s atmosphere: 100 days of sunspots Sunspots are darker patches on the sun’s surface. It would create waves that can carry huge amounts of energy along vast distances – from the sun’s surface to its upper atmosphere. He reasoned that within the sun’s magnetized plasma any bulk motions of electrically charged particles would disturb the magnetic field. They 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.Ĭonvection drags these fields up from the sun’s interior. 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. 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, scientists have consistently estimated the photosphere’s temperature at around 6,000 degrees C (11,000 degrees F). 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. Estimating the photosphere’s heat has always been relatively straightforward. 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. That’s 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. The coronal heating problem has been established since the late 1930s. It has validated Alfvén’s 80-year-old theory and taken us a step closer to harnessing this high-energy phenomenon here on Earth. Our recent study has finally achieved this. We needed empirical observation that these waves existed. Scientists had tentatively accepted the theory, but we still needed proof. The energy bypasses the photosphere before exploding with heat in the sun’s upper atmosphere. He theorized that magnetized waves of plasma could carry huge amounts of energy along the sun’s magnetic field from its interior to the corona. In 1942, the Swedish scientist Hannes Alfvén proposed an explanation. It represents a fundamental puzzle that astrophysicists have mulled over for decades.
This spike in temperature, despite the increased distance from the sun’s main energy source, has been observed in most stars. The corona reaches a million degrees C or higher (over 1.8 million degrees F). But a few thousand kilometers above it – a small distance when we consider the size of the sun – the solar atmosphere, also called the corona, is hundreds of times hotter. The visible surface of the sun, or the photosphere, is around 6,000 degrees Celsius (11,000 degrees Fahrenheit). The sun’s atmosphere via Mongta Studio/ Shutterstock.īy Marianna Korsos, Aberystwyth University and Huw Morgan, Aberystwyth University Burning questions about the sun’s atmosphere
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