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Fixing A part of the “Photo voltaic Drawback”

Sun Model Structure

The mannequin developed by the scientists contains the historical past of the rotation of the solar but additionally the magnetic instabilities that it generates. Credit score: Sylvia Ekström / UNIGE

A world group of astronomers has succeeded in growing a mannequin to resolve a part of the “photo voltaic downside.”

All was fallacious with the Solar! A brand new set of knowledge within the early 2000s introduced down the chemical abundances on the floor of the Solar, contradicting the degrees predicted by the usual fashions utilized by astrophysicists. Incessantly challenged, these new abundances made it by a number of new analyses. As they appeared to show right, it was thus as much as the photo voltaic fashions to adapt, particularly since they function a reference for the research of stars generally. A group of astronomers from the UNIGE in collaboration with the Université de Liège, has developed a brand new theoretical mannequin that solves a part of the issue: contemplating the Solar’s rotation, which diversified by time, and the magnetic fields it generates, they’ve been capable of clarify the chemical construction of the Solar. The outcomes of this research are revealed within the journal Nature Astronomy.

“The Solar is the star that we will greatest characterize, so it constitutes a basic take a look at for our understanding of stellar physics. We’ve got abundance measurements of its chemical parts, but additionally measurements of its inner construction, like within the case of Earth due to seismology,” explains Patrick Eggenberger, a researcher on the Division of astronomy of the College of Geneva, Switzerland (UNIGE) and first creator of the research.

These observations ought to fall in keeping with the outcomes predicted by the theoretical fashions which purpose at explaining the Solar’s evolution. How does the Solar burn its hydrogen within the core? How is vitality produced there after which transported in the direction of the floor? How do chemical parts drift throughout the Solar, influenced each by rotation and magnetic fields?

The usual photo voltaic mannequin

“The usual photo voltaic mannequin we used till now considers our star in a really simplified method, on the one hand with regard to the transport of the chemical parts within the deepest layers, then again for the rotation and the inner magnetic fields that have been completely uncared for till now,” explains Gaël Buldgen, a researcher on the Division of astronomy of the UNIGE and co-author of the research.

Nevertheless, all the pieces labored effective till the early 2000s, when a global scientific group drastically revised the photo voltaic abundances due to an improved evaluation. The brand new abundances precipitated deep ripples within the waters of the photo voltaic modeling. From then on, no mannequin was capable of reproduce the info obtained by helioseismology (the evaluation of the Solar’s oscillations), particularly the abundance of helium within the photo voltaic envelope.

A brand new mannequin and the important thing position of rotation and magnetic fields

The brand new photo voltaic mannequin developed by the UNIGE group contains not solely the evolution of rotation which was most likely sooner up to now, but additionally the magnetic instabilities it creates. “We should completely think about concurrently the consequences of rotation and magnetic fields on the transport of chemical parts in our stellar fashions. It is necessary for the Solar as for stellar physics generally and has a direct influence on the chemical evolution of the Universe, on condition that the chemical parts which are essential for all times on Earth are cooked within the core of the celebrities,” says Patrick Eggenberger.

Not solely does the brand new mannequin rightly predict the focus of helium within the outer layers of the Solar, however it additionally displays that of lithium which resisted modeling till now. “The abundance of helium is appropriately reproduced by the brand new mannequin as a result of the inner rotation of the Solar imposed by the magnetic fields generates a turbulent mixing which prevents this ingredient from falling too shortly in the direction of the middle of the star; concurrently, the abundance of lithium noticed on the photo voltaic floor can also be reproduced as a result of this identical mixing transports it to the recent areas the place it’s destroyed,” explains Patrick Eggenberger

The issue shouldn’t be totally resolved

Nevertheless, the brand new mannequin doesn’t remedy each problem raised by helioseismology: “Because of helioseismology, we all know inside 500 km through which area the convective actions of matter start, 199,500 km under the floor of the Solar. Nevertheless, the theoretical fashions of the Solar predict a depth offset of 10,000 km!” explains Sébastien Salmon, researcher on the UNIGE and co-author of the paper. If the issue nonetheless exists with the brand new mannequin, it opens a brand new door of understanding: “Because of the brand new mannequin, we make clear the bodily processes that may assist us resolve this crucial distinction.”

Replace of solar-like stars

“We’re going to need to revise the plenty, radii, and ages obtained for the solar-type stars that now we have studied to date,” says Gaël Buldgen, detailing the subsequent steps. Certainly, most often, photo voltaic physics is transposed to case research near the Solar. Due to this fact, if the fashions for analyzing the Solar are modified, this replace should even be carried out for different stars just like ours.

Patrick Eggenberger specifies: “That is notably essential if we wish to higher characterize the host stars of planets, for instance throughout the framework of the PLATO mission.” This observatory of 24 telescopes ought to fly to the Lagrange level 2 (1.5 million kilometers from Earth, reverse the Solar) in 2026 to find and characterize small planets and refine the traits of their host star.

Reference: “The inner rotation of the Solar and its hyperlink to the photo voltaic Li and He floor abundances” by P. Eggenberger, G. Buldgen, S.J.A.J. Salmon, A. Noels, N. Grevesse and M. Asplund, 26 Might 2022, Nature Astronomy.
DOI: 10.1038/s41550-022-01677-0



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