Science. – A model that successfully solves part of the “solar problem” – Publimetro México

Madrid, 31 (European press)

In the early 2000s, a new data set revised the chemical abundance on the Sun’s surface, contradicting values ​​predicted by standard models used by astrophysicists. This new exuberance has often been challenged, outperforming various analyses. As it seemed correct, it was up to the solar models to adapt, especially as they serve as a reference for the study of stars in general. The new model, described in Nature Astronomy, addresses the question.

“The Sun is the star we can best distinguish, so it is a fundamental test of our understanding of stellar physics. We have abundant measurements of its chemical elements, but also of its internal structure, as in the case of the Earth thanks to seismology,” explains Patrick Eggenberger, researcher in the Department of Astronomy at the University of Geneva (University of Geneva) and first author of the study.

These observations should be in line with the results predicted by theoretical models aimed at explaining the evolution of the Sun. How does the sun burn hydrogen in the heart? How is energy produced there and then transferred to the surface? How do chemical elements move within the sun, affected by both rotation and magnetic fields?

“The standard solar model that we have used so far considers our star in a very simplified way, on the one hand, in terms of the transport of chemical elements in the deep layers; and on the other, in terms of rotation and internal magnetism which have been completely neglected until now,” explains Gail Boldgen, researcher in the Department of Astronomy at UNIGE and co-author of the study.

All went well, until the early 2000s, when an international scientific team radically revised the abundance of solar energy thanks to improved analysis. The new abundance caused deep ripples in the solar modeling waters. Since then, no model has been able to reproduce the data obtained by heliosmology (analysis of the sun’s oscillations), in particular the abundance of helium in the heliosphere.

The new solar model developed by the UNIGE team includes not only the evolution of the spin, which may have been faster in the past, but also the magnetic instability that it created. “We must simultaneously look at the effects of rotation and magnetic fields on the transport of chemical elements in our stellar models. It is important for the Sun as well as for stellar physics in general and has a direct impact on the chemical evolution of the universe, given that the chemical elements necessary for life on Earth are cooked up in the core of stars ‘ says Patrick Egenberger.

The new model not only correctly predicts the concentration of helium in the outer layers of the Sun, but also reflects the concentration of lithium, which has been reluctant to design the model until now. “The abundance of helium is properly produced by the new model because the internal rotation of the Sun imposed by magnetic fields generates a turbulent mixing that prevents this element from falling too rapidly towards the center of the star; at the same time, an abundance of lithium is observed in the Sun also reproduces the surface because this same mixture It transports it to warm regions where it is destroyed,” explains Patrick Eggenberger

However, the new model does not solve all the challenges posed by helioscience: “Thanks to helioscience, we know in 500 km in which region the convective motions of matter begin, at a depth of 50,000 km below the surface of the Sun. However, theoretical models of the Sun predict a deep displacement of 10,000 km”, says Sebastien Salmon, researcher at UNIGE and co-author of the article. If the problem persists with the new paradigm, it opens a new door to understanding: “Thanks to the new paradigm, we are shedding light on physical processes that can help us resolve this important difference.”

“We will have to review the masses, radii and ages obtained for the stars of the solar type that we have studied so far,” says Gaël Buldgen, detailing the following steps. In fact, in most cases, solar physics is transferred to case studies near the Sun. Therefore, if the models are modified to analyze the Sun, this update should also be carried out for other stars similar to ours.

“This is especially important if we want to better characterize the planet’s host stars, for example within the framework of the Plato mission,” says Patrick Eggenberger. This observatory of 24 telescopes must fly to Lagrange Point 2 (1.5 million kilometers from Earth facing the Sun) in 2026 to discover and characterize minor planets and tune into the properties of their host star.