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The Sun is rebooting

Every 11 years the Sun needs a reset, and it has been occurring since we have had the instrumentation to measure it, perhaps even before

The Sun
Recreation of the European Space Agency's Solar Orbiter mission.ESA

“Chaos is an order to be deciphered,” wrote José Saramago. That’s exactly where the Sun is right now, in chaos. It is not the first time, nor will it be the last. It is a growing chaos that is leading to the need for a reboot, like pressing the reset button on an electronic device. The comparison is not very far removed from reality, since what is happening to the Sun right now is related to something amazing and almost magical: the magnetic field.

Let me start with a typical joke that circulates among astrophysicists. Whenever an astrophysicist presents a model of how a galaxy forms, or how a star evolves, the first question should be: have you taken magnetic fields into account? The answer is not usually positive.

Magnetic fields, whose effects we have known about for millennia — from the existence of Chinese compasses made in the 2nd century B.C. — are difficult to model. They are everywhere and we don’t value them enough, poor things. From when we wake up in the morning and switch off our alarm to when we fall asleep when we turn on the TV (at least I do!), and let’s not forget when we vacuum or put on the washing machine, everything is has a connection to magnetic fields. They seem to work like magic because they are not easy to understand. Who can say that they have never played with a magnet as a child? And who has not been surprised by how magnets can make metals move, and also turn some them into magnets too? Indeed, the complicated thing about magnetic fields is that they alter matter and turn it into the creator of more magnetic fields, especially if we are talking about matter in which electrons and protons are not closely linked.

We cannot understand how the Sun works without studying its magnetic field. Or, rather, we usually say their magnetic fields, because the subject is so complicated that a lot of effects must be considered. Not in vain, the temperature of the surface of the Sun is about 5,800 degrees Celsius and that temperature grows towards its core, which reaches 15 million degrees. On the outside, towards what is called the corona, the temperature reaches one million degrees. At these temperatures many electrons cannot stay bound to their nuclei, and the material is said to be ionized. And the mixture of electrons and nuclei that can move freely in a medium that is globally neutral (that is, there are the same number of electrons as protons) is called plasma.

The Sun’s magnetic field, as if it were that magnet acting on a pin, creates movements in material. But the movements of plasma material are like an electric current, which creates its own field on a smaller scale, like the pin being turned into a magnet. Furthermore, in the Sun material moves for other reasons, such as convection, in a manner similar to the movement of water in a boiling pot, with the hottest material rising towards the surface, cooling, and then sinking back down. And a moving ionized material creates magnetic fields. In short, the Sun is a jumble of magnetic fields, forgive the non-scientific word, but it is very appropriate.

How do we notice that the Sun is a great creator of magnetic fields? Well, this year we have been able to see the northern lights in central Spain. Data at more normal, northerly latitudes indicate that we can enjoy the brightest auroras in the last 20 years. These auroras come from the ionized material ejected from the Sun due to its intense magnetic fields interacting with the Earth’s magnetosphere, which also has its own magnetic field! The charged particles of the Sun are directed towards the poles by the magnetosphere, and there they collide with atoms in the upper atmosphere, giving energy to the electrons of matter such as oxygen, and these electrons then tend to go where they should, and bind with their nuclei. In the process, they emit the beautiful green lights of the Northern Lights, as the result of something as simple as energy conservation. The intensity of the auroras depends on the amount of material ejected by the Sun, and this is triggered in what are called solar eruptions, which cause magnetic storms on the planets.

To date, in 2023 we have had 11 of the most intense type X eruptions, whereas in 2022 we had only seven, and in 2021, only two. As for the weaker types, such as M, C, and B (each one decreasing in intensity by a factor of 10) they are also breaking records. In both 2022 and 2023 we have had type X2, and this August an eruption caused a solar storm on Earth that caused the loss of navigation satellite signals for almost 2 hours in the area of the Earth facing the Sun.

All of this is telling us that the Sun is increasing its activity significantly, following a cycle that we know lasts 11 years. Because the Sun, although it emits energy in a fairly constant manner (with fluctuations of less than 1%), is not a calm star. Its activity is reflected in its appearance in different ways, with characteristics such as the spots and solar flares. The current cycle will continue until it reaches its maximum, scheduled for July 2025, but which could be coming sooner, since the Sun has been more active since mid-2022 than at the last maximum that occurred in 2014.

The Sun’s cycle is governed by magnetic fields. It all starts from a relatively calm situation where the photosphere, which is what we see of the Sun directly, and which explains daylight, is not affected by any magnetic effects. But suddenly, flows of material from the Sun’s interior reach the photosphere, and bring new magnetic fields. That’s what causes sunspots. As the number of spots grows and grows, the magnetic fields become increasingly more intense and complicated in the external parts of the Sun. Flares and expulsions of material then begin to occur, especially from the corona, where the temperatures are very high and magnetic fields have dramatic effects.

And the “jumble” that was mentioned above reaches its climax, at which point… the Sun restarts! The magnetic fields disappear from the photosphere, we no longer see spots, the eruptions decrease until they disappear. And, in the same process, it seems incredible, the Sun’s general magnetic field is reversed. What was the magnetic north pole, from which charged particles move away, becomes south, and south becomes north. From chaos a new, much calmer order will emerge until 11 years from now, when we return to the same situation.

To observe the Sun, you can use a pair of binoculars — very carefully and never looking directly through them — to project an image of the Sun onto a piece of cardboard. You will need to focus the image by moving the cardboard nearer or farther away from the binoculars, and it is better to look at the projection in the shade. An alternative is to buy a mini-solar telescope. Every school should have one to teach about the source of energy for all life. Either way, you will be able to see quite a few sunspots these days. For more details, and if the reader is curious about other characteristics of our nearest star, such as flares, they can check out the daily images of the Sun taken by NASA using different instruments. And we invite curious observers to think that what they are seeing is a great jumble of magnetic fields that is currently being reset, with a reversal of polarity happening in a 1.4 million kilometer star, a tiny magnet.

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