Mapping the Hidden Magnetic Field of the Quiet Sun

Abstract

The Sun is the only star where we can resolve the intricate magnetism that all convective stars harbor. Yet, more than 99% of its visible surface along the solar cycle (the so-called quiet Sun) is filled with a tangled, unresolved magnetism. These "hidden" fields are thought to store enough magnetic energy to play a role in the heating of the Sun's outer atmosphere, but its field strength is still not constrained. Previous investigations based on the Hanle effect in atomic lines claim a strong magnetization of about 100 G, while the same effect in molecules show a factor of 10 weaker fields. The discrepancy disappears if the magnetic field strength of the hidden is not homogeneous in the solar surface. In this letter, we prove using magnetohydrodynamical simulations that it is possible to infer the average field strength of the hidden quiet Sun magnetic fields using multi-line inversions of intensity profiles in the Zeeman regime. Using this technique with 15 spectral lines in the 1.5 µm spectral range, we reveal that the spatial distribution of the hidden field is strongly correlated with convection motions, and that the average magnetization is about 46 G. Reconciling our findings with the Hanle ones is not obvious and will require future work on both sides, since it implies an increase of the field strength with height, something that is physically questionable.

The European Solar Telescope

“…Through the analysis of inversion codes (del Toro Iniesta & Ruiz Cobo 2016; de la Cruz Rodríguez & van Noort 2017), one could investigate whether two decoupled atmospheric components are required when reproducing many simultaneously observed spectral lines from the radiation emerging from the model atmosphere. There is still some work be done to characterise the 'response' (Landi Degl'Innocenti & Landi Degl'Innocenti 1977) of candidate spectral lines to changes in the atmospheric parameters to create a comprehensive selection of candidate transitions with different ionisation stages that would be optimised to study these phenomena (see, for example, Socas-Navarro et al 2008;Demidov & Balthasar 2012;Kuckein et al 2021;Trelles Arjona et al 2021).…”

Global Impact of Emerging Internetwork Fields on the Low Solar Atmosphere

“…Internetwork (IN) magnetic fields are dynamic magnetic structures that populate the interior of supergranular cells (Livingston & Harvey 1975;Smithson 1975). They are spread all over the Sun (Wang et al 1995), maintain the photospheric network (NW; Gošić et al 2014), and may hold a significant fraction of the total magnetic energy stored at the solar surface (Trujillo Bueno et al 2004;Trelles Arjona et al 2021). For these reasons, IN fields are considered to be the main building blocks of the quiet-Sun (QS) magnetism (see Bellot Rubio & Orozco Suárez 2019 for a review).…”

An Iterative OLA Method for Inversion of Solar Spectropolarimetric Data. I. Single- and Multiple-variable Inversions of Thermodynamic Quantities

“…Further, the observed intensity is a weighted integral of the physical properties of the atmosphere over a range of depths, and thus multiple inversion solutions are consistent with a given observed spectrum. Nonetheless, within the model assumptions, solar inversions have yielded valuable information about the morphology of sunspots (e.g., Collados et al 1994;Solanki 2003;Orozco Suarez et al 2005;Borrero & Ichimoto 2011;Borrero et al , 2019Borrero et al , 2021, properties of the quiet-Sun magnetism (e.g., Stenflo 1982;Trujillo Bueno et al 2004;Martínez González et al 2008;Lites et al 2008;Stenflo 2010;Bellot Rubio & Orozco Suárez 2019;Trelles Arjona et al 2021), and the multithermal structure of the solar chromosphere (e.g., Asensio Casini et al 2009;Bueno 2010;Priest et al 2018;Yadav et al 2020;Anan et al 2021;Morosin et al 2022), as examples.…”