The difficulty of reconstructing the sun in the laboratory


Technology Innovation Website Editor – 06/17/2022

The model resolves most of the inconsistencies between theory and observations – but not all.
[Imagem: Sylvia Ekstrm/UNIGE]

sun model

Over the past two decades, a series of space probes, telescopes and new equipment on the ground have measured chemical elements present in the Sun with unprecedented precision, giving us unprecedented information about our star.

The problem is that these new data systematically contradict the values ​​predicted by the models astrophysicists use to explain the composition and behavior of the Sun.

Given the new observational data, no model has been able to reproduce the data obtained through helioseismology (analysis of solar oscillations), in particular the abundance of helium and lithium in the solar envelope.

“The standard solar model we have used so far has considered our star in a very simplified way, on the one hand about the transport of chemical elements in the deeper layers, and on the other hand with regard to the rotation and internal magnetic fields, which until now have are completely ignored,” explains Gal Buldgen, a researcher at the University of Geneva in Switzerland.

Now, astrophysicists have finally managed to build a model that explains at least most of the mismatch between theory and observations: Given the sun’s rotation, its speed has been changing over eons, and how much it produces of the magnetic field, the team managed to explain the chemical structure of the sun.

The difficulty of reconstructing the sun in the laboratory

The researchers used experiments in a “stellar simulator” to demonstrate the explanatory power of their new model.
[Imagem: ANU]

Helium and Lithium in the Sun

The new Sun model includes not only the evolution of the star’s rotation (which may have been faster in the past), but also the magnetic instabilities it creates.

“In our stellar models, we must absolutely simultaneously account for the effects of rotation and magnetic fields on the transport of chemical elements. This is important for the Sun, as it is for stellar physics in general, and has a direct impact on the chemical evolution of the universe, given that Chemicals vital to life on Earth are baked into the cores of stars,” Professor Patrick Eggenberger gave in context – see Periodic Table of Elements Born in Stars.

Not only did the new model correctly predict the concentration of helium in the sun’s outer layers, but it also reflected the concentration of lithium, which all modeling to date has resisted.

“The new model correctly reproduces the abundance of helium because the internal rotation of the Sun imposed by the magnetic field creates turbulent mixing that prevents this element from falling too quickly towards the center of the star; at the same time, the observed lithium abundance of material on the Sun’s surface is also replicated because the same mixture transported it to hot regions where it was destroyed,” Eggenberger detailed.

The difficulty of reconstructing the sun in the laboratory

not everything is resolved

However, even the new model cannot address all the challenges posed by helioseismology:

“Because of helioseismology, we know that the convective motion of matter begins at a region of 500 kilometers, 199,500 kilometers below the Sun’s surface. However, theoretical models of the Sun predict a depth displacement of 10,000 kilometers!” said Sbastien Salmon, co-author of the model.

“We’re going to have to review the masses, radii, and ages of the solar-type stars we’ve studied so far,” Buldgen said, detailing the team’s next steps.

In fact, for the most part, solar physics is diverted to studying other stars. Therefore, if the analytical model of the sun is modified, other stars like ours must also undergo this update.


article: The internal rotation of the sun and its connection to the solar lithium and helium surface abundances
Authors: P. Eggenberger, G. Buldgen, SJAJ Salmon, A. Noels, N. Grevesse, M. Asplund
Magazine: Nature Astronomy
DOI: 10.1038/s41550-022-01677-0

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