Shedding light on the Sun

For most of human history, it has been difficult to offer an explanation of the Sun without recourse to deities.

In ancient Greece, for example, the god Helios, the personification of the Sun, traveled the heavens in his chariot to create night and day, while in ancient Egypt Ra, the god of the Sun with falcon head

Since then, science has revealed, among other things, that the Sun rotates on its axis, on average, once every 28 days.

However, at the equator, this sphere of hot plasma rotates once every 25 days, while at the poles it rotates approximately every 35 days, thus contributing to the creation of a hot plasma maelstrom.

Despite this, the power of the Sun and its ferocious eruptions, which have come to fry communication satellites and other electronic instruments on Earth, may still hold surprises.

The scientific community warns that solar flares will gain momentum as a peak of activity approaches, expected at the end of 2024 and the beginning of 2025.

"Inside our star, a turbulent movement takes place, called convection, which is somewhat similar to that of hot water just before it boils," says Professor Sacha Brun, director of research at the CEA Paris-Saclay center, of the commission French Atomic Energy and Alternative Energies.

A famous magnetic storm that struck Earth in September 1859, known as the Carrington event, unleashed splendid aurorae in regions far from the poles and caused sparks to spark from telegraphs around the world.

Since then, there have been others.

In 1989, a geomagnetic storm caused a blackout in Quebec, Canada, recalls Brun.

To predict and understand these events, we must acquire a more comprehensive knowledge of the Sun. This impetuous sphere of hydrogen and helium also reaches unimaginable temperatures, reaching 15 million degrees at its core, and is enormous in size: more than a million Earths would fit inside the Sun.

Its peaceful presence on sunny days hides the intense nuclear reactions that occur at its center, generating vast amounts of energy.

The Sun is a churning sphere of plasma, whose gases are so hot that electrons leave atoms and produce intense magnetic explosions on the surface, from which millions of tons of matter are spewed into space.

a magnetic charm

As it rotates, the Sun's mechanical energy is converted to magnetic energy, much like a bicycle dynamo works, transforming the motion of the pedal into magnetic energy.

On the Sun, sinuous bands of magnetism rise up, producing sunspots on the surface, dark areas in which the magnetic field is 3,000 times stronger than in the surrounding areas.

Sunspots can generate those flares that damage electrical devices.

However, this activity is not constant.

"The Sun's magnetism varies over an 11-year cycle," says astrophysicist Brun. During this cycle, coronal mass ejections go from once every three days to three times a day at their peak.

“As the cycle progresses, the frequency of the eruptions increases,” Brun says.

"People are not aware that the Earth is immersed in the turbulent magnetic sphere of our star."

Therefore, the need to anticipate these solar storms is indisputable.

In February 2022, for example, a solar flare destroyed the electronic circuitry of 40 commercial SpaceX satellites, rendering them unusable.

More information

What will happen to the Sun when it runs out of hydrogen?

Those energetic particles take only 15 minutes to travel from the Sun to the Earth.

By contrast, the threat posed by magnetic clouds usually takes several days to materialize, giving us more room to prepare.

Brun co-leads an EU-funded project, WHOLE SUN, which aims to understand the inner and outer layers of the only star in Earth's solar system.

With an execution period of seven years, this initiative, which will run until April 2026, focuses on the turbulent movement of the interior of the Sun and the complex physical processes that convert this internal turmoil into magnetism in the outer layers.

The study requires the most powerful supercomputers in the world, since the task is not minor: the prediction of solar flares will mean a significant improvement in the understanding of the interior of the Sun by the scientific community.

The birth of a star

What was the Sun's distant past like?

Its existence dates from 4.6 billion years ago, 100 million years before that of the Earth.

The process that gave rise to its formation and the place where it happened might seem like an impenetrable mystery.

However, according to Dr. Maria Lugaro from the Konkoly Observatory of the Hungarian Academy of Sciences, this is not the case.

Lugaro, an Italian astrophysicist, is investigating this issue within the framework of the EU-funded RADIOSTAR project, launched in 2017 and running until August of this year.

"We believe that the Sun was not born alone, but in a star-forming region with a high presence of stars," says Lugaro.

Lugaro delves into the Sun's past by examining the chemical fossils present in current meteorites.

Radioactive atoms are unstable.

In a certain period of time, they release energy and disintegrate into so-called daughter nuclides, which are measurable.

These children are, consequently, chemical fossils that provide information about radioactive atoms existing in another era.

Lugaro's research suggests that the Sun formed in a stellar nursery containing sister stars, including supernova stars, also known as stellar explosions.

However, digging into the Sun's past requires meteorites, chunks of rock formed before Earth.

These meteorites may contain trace amounts of radioactive atoms, such as aluminum-26 or hafnium-182.

It is known that these atoms existed only in a certain period of time.

Combined, the traces of these atoms can work like a radioactive clock, calculating the age of the stars that formed them relative to the age of the Sun.

a vivid speech

Some radioactive atoms are found only in certain types of stars, so their presence in meteorites helps recreate how the Sun was born, although the findings are open to debate.

It may be that the Sun formed in a stormy region, among clouds of dust and gas and next to supergiant stars and supernovae.

Within about 20 million years, the various stars would have begun to leave the nursery.

However, from a scientific point of view, there is nothing conclusive.

"Every year there is a debate. Is the Sun a rare or normal star?" Lugaro exemplifies.

"It is fun!".

The research described in this article has been funded by the European Research Council (ERC).

Article originally published in

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