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In 1998, scientists reported the detection of a mysterious signal by analyzing the polarization of sunlight. The only explanation that could be found implied that the solar chromosphere is virtually unmagnetized, contradicting other evidence.
This mysterious linear polarization signal, produced by diffusion processes, appears at the wavelength of a neutral sodium line (known as the D1 line), where such diffusion polarization should not be present.
This paradox has led scientists to perform many laboratory experiments. But, instead of obtaining a solution, the paradox raised many questions. This opened up a paradox that challenged physicists for many years.
Scientists from the Istituto Ricerche Solari (IRSOL) in Locarno-Monti and the Instituto de Astrofísica de Canarias (IAC) in Tenerife have discovered a solution to this paradox. Their solution provides an excellent opportunity for scientists to explore the elusive magnetic fields of the solar chromosphere in today’s new era of large aperture solar telescopes.
For the study, the scientists carried out an advanced theoretical modeling of the polarization of the solar line D1 never attempted. It is also three years of work carried out in close collaboration between the Istituto Ricerche Solari (IRSOL) of Locarno-Monti (affiliated to the USI Università Della Svizzera Italiana) and the POLMAG group of the Instituto de Astrofísica de Canarias (IAC) in Tenerife.
Scientists have noted, “This result has important consequences. Scattered polarization signals, like that seen in the D1 sodium line, are exciting because they encode unique information about the elusive magnetic fields present in the solar chromosphere.
“This key interface layer of the solar atmosphere, located between the underlying cooler photosphere and the overlying million-degree corona, is at the heart of several persistent problems in solar physics, including understanding and the prediction of eruptive phenomena that can strongly impact our technology-dependent society. The magnetic field is the main driver of the spectacular dynamic activity of the solar chromosphere. However, our empirical knowledge of its intensity and geometry is still largely unsatisfactory .
“The solution of the long-standing paradox of the polarization of the solar line D1 proves the validity of the current quantum theory of the polarization of the spectral line and opens a new window to explore the magnetism of the solar atmosphere in the current new era large aperture solar power telescopes.
Journal reference:
- Ernest Alsina Ballester et al., Solving the paradox of polarization of the solar sodium D1 line, Physical Review Letters (2021). DOI: 10.1103 / PhysRevLett.127.081101
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