Solving the paradox of the solar sodium D1 line polarization

TL;DR

This paper resolves a long-standing paradox by showing that the polarization signals in the sodium D1 line can be explained with weak magnetic fields, revealing new insights into solar chromosphere magnetism.

Contribution

It provides the first explanation of the sodium D1 line polarization signals considering magnetic fields, challenging previous assumptions of an unmagnetized chromosphere.

Findings

Polarization signals explained by magnetic fields in the gauss range

Reveals the presence of magnetism in the solar chromosphere

Opens new diagnostic possibilities for solar magnetism

Abstract

Twenty-five years ago, enigmatic linear polarization signals were discovered in the core of the sodium D1 line. The only explanation that could be found implied that the solar chromosphere is practically unmagnetized, in contradiction with other evidences. This opened a paradox that has challenged physicists for many years. Here we present its solution, demonstrating that these polarization signals can be properly explained in the presence of magnetic fields in the gauss range. This result opens a novel diagnostic window for exploring the elusive magnetism of the solar chromosphere.