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Solar mystery solved: Sun’s rotation has slowed with time — explains surface composition | Science | News


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The study was undertaken by astrophysicist Dr Patrick Eggenberger of the University of Geneva (UNIGE) and his colleagues. Dr Eggenberger said: “The Sun is the star that we are able to best characterise, so it constitutes a fundamental test for our understanding of stellar physics. “We’ve abundance measurements of its chemical elements, but additionally measurements of its internal structure, like within the case of Earth because of seismology.”

Ideally, all of those real-world measurements would match the Sun’s properties as predicted by the models that physicists have created to clarify the star’s evolution.

These models help scientists investigate questions from how the Sun burns hydrogen in its core to how chemical elements move across the star.

Until the early 2000s, the usual solar model held up quite well — until a world team published revised measurements of the chemical abundances on the Sun’s surface that clashed with those predicted by the model.

Since then, the proposed recent abundance values have survived various verifications, suggesting that the issue must lie with the solar model itself.

A discrepancy between models and measurements of the Sun has finally been solved (Image: Getty Images)

An infographic about the Sun

Dr Eggenberger said: ‘The Sun is the star that we are able to best characterise’ (Image: Express.co.uk)

Paper co-author and astronomer Gaël Buldgen, also of UNIGE, said: “The usual solar model we used until now considers our star in a really simplified manner.”

This oversimplification, she explained, applies to each how chemical elements are transported inside the Sun’s deepest layers, but additionally to how the Sun rotates and the character of the inner magnetic fields that it generates.

Various recent models have been proposed over the past 20 years which have strived to clarify the brand new chemical abundance measurements.

Nonetheless, until now, none had managed to adequately reproduce the info obtained from so-called helioseismology — the name given to the evaluation of the Sun’s oscillations — specifically as related to the abundance of helium within the Sun’s convective outer layers.

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An artist's impression of a young Sun-like star

The team assumed the Sun initially rotated five times faster than its equatorial rotation rate now (Image: Getty Images)

The brand new model proposed by Dr Eggenberger and his colleagues has reconciled these differences by considering each the evolution of the Sun’s rotation — which they consider was likely faster prior to now — but additionally the magnetic instabilities such creates.

Of their model, the team assumed that the Sun was initially rotating around five times faster than its present-day equatorial rotation rate.

As Dr Eggenburger said: “We must absolutely consider concurrently the results of rotation and magnetic fields on the transport of chemical elements in our stellar models.

“It’s as necessary for the Sun as for stellar physics basically, and has a direct impact on the chemical evolution of the Universe, on condition that the chemical elements which are crucial for all times on Earth are cooked within the core of the celebs.”

A cutaway of the Sun

The brand new model explains the abundances of helium and lithium within the solar envelope (Image: Sylvia Ekström / UNIGE)

Based on the team, their recent model not only accurately predicts the concentrations of helium within the solar envelope, but additionally that of lithium, one other element whose measured abundances on the Sun’s surface had previously proven difficult to match in models.

Dr Eggenburger explained: “The abundance of helium is appropriately reproduced by the brand new model because the inner rotation of the Sun imposed by the magnetic fields generates a turbulent mixing.”

This, he added, “prevents this element from falling too quickly towards the centre of the star.

“Concurrently, the abundance of lithium observed on the solar surface can be reproduced because this same mixing transports it to the recent regions where it’s destroyed.”

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An artist's impression of PLATO

The findings may inform PLATO (pictured), whose mission involves studying exoplanets and their stars (Image: ESA)

The brand new model, nonetheless, doesn’t resolve all the problems.

Paper creator and UNIGE astronomer Dr Sébastien Salmon explained: “Due to helioseismology, we all know inside 500 km [311 miles] through which region the convective movements of matter begin, 199,500 km [123,964 miles] below the surface of the Sun.

“Nonetheless, the theoretical models of the Sun predict a depth offset of 10,000 km [6,214 miles]!”

“Due to the brand new model, we make clear the physical processes that will help us resolve this critical difference.”

The findings can even have an effect on our understanding of all the opposite Sun-like stars now we have studied so far — as physicists have long drawn inferences about their properties and behavior based on how we thought the Sun behaved.

Dr Buldgen said: “We’re going to must revise the masses, radii and ages obtained for the solar-type stars that now we have studied thus far.”

Dr Eggenberger added: “This is especially necessary if we wish to raised characterise the host stars of planets, for instance inside the framework of the PLATO mission.”

PLATO — short for “PLAnetary Transits and Oscillations of stars” — is a European Space Agency mission, as a consequence of launch in 2026.

It’s going to see an area observatory with 26 telescopes sent to a degree in space 932,057 miles from Earth to find and study small planets and analyse the characteristics of their host stars.

The total findings of the study were published within the journal Nature Astronomy.

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