Image of the solar atmosphere showing coronal mass ejection. Credit: NASA/GSFC/SDO
Nature published a landmark letter in 1998 that stated that a mysterious signal was discovered during polarization analysis. This signal implied that the solar chromosphere, an important layer of the sun's atmosphere, is virtually unmagnetised. This contradicts common wisdom. This paradox prompted laboratory experiments and theoretical investigations that, instead of finding a solution to the problem, brought up new questions and led some scientists even to question the quantum theory on matter-radiation interaction.
Researchers at the Istituto ricerche Solari in Locarno-Monti, affiliated to the USI Universit della Svizzera italiana, and the Instituto de Astrofsica de Canarias in Tenerife have discovered the answer to this paradox. This opens up a new window to explore the mysterious magnetic fields of the solar chromosphere during the new era large-aperture solar telescopes. Physical Review Letters published their findings.
Twenty-five year ago, an enigmatic signal, discovered during the analysis of the polarization sunlight using a new instrument, called the Zurich Imaging Polarimeter, (ZIMPOL), which was developed at ETH Zurich, and later installed at IRSOL. The mysterious linear polarization signal is caused by scattering and appears at the wavelength a neutral sodium line (the D1 line). Quantum mechanics says that there should not be any scattering polarization. The signal was completely unexpected and sparked intense scientific debate. Two years later, Nature published an explanation that suggested that the chromosphere layer of the sun's atmosphere was not magnetized. This contradicts previous results. Researchers believed that this area is permeated with magnetic fields in the gauss region. These new findings have opened up a paradox that has been challenging solar physicists over many years. They also led scientists to question the existing quantum theory of matter radiation interaction.
In a paper published in Physical Review Letters Ernest Alsina Ballester (IRSOL (IAC), Luca Belluzzi(IRSOL) and Javier Trujillo Bueno (“IAC”) present the solution to this fascinating paradox. These findings were made possible by the most sophisticated theoretical modeling of solar D1 line polarization. This involved three years of work in close collaboration between the Istituto Ricerche Solari in Locarno–Monti (affiliated with the USI Universit della Svizzera italiana), and the POLMAG group at the Instituto de Astrofsica de Canarias in Tenerife.
Researchers explain that this result has important implications. Because they contain unique information about the mysterious magnetic fields in the solar chromosphere, scattering polarization signals such as the one seen in the D1 sodium line are very interesting. This layer, which is the interface layer between the solar atmosphere's cooler photosphere and its overlying million degree corona, is the heart of many enduring problems in solar Physics. It also helps to predict and understand the effects of eruptive phenomena on our technologically dependent society. Although the magnetic field is well-known to be the primary driver of the extraordinary dynamical activity in the solar chromosphere's solar chromosphere it is not clear how much or what its geometry and intensity are. The long-standing paradox of solar line polarization D1 has been solved. This opens up new possibilities to study the magnetism in the solar atmosphere using large-aperture solar telescopes.
Further explorations of CLASP-2: Exploring the magnetic solarchromosphere
More information: Ernest Alsina Ballester et., Solving The Paradox of Solar Sodium Line Polarization, Physical Review Letters (2021). Information from the Journal: Nature, Physical Review Letters Ernest Alsina Ballester et. al. Solving the Paradox Of The Solar Sodium D1-Line Polarization, (2021). DOI: 10.1103/PhysRevLett.127.081101
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