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One of the greatest mysteries of contemporary science is called ‘Solar corona heating problem’. And it can be summarized as follows: in the Sun, which is a huge sphere of incandescent gas – in a state called plasma – contrary to what logic would dictate, the temperature increases as we move away from its surface , passing from the photosphere to the solar corona.
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To understand it better, an analogy can be made between the star king and a fireplace, which is a source of thermal energy. If you move away from the campfire, expect the temperature to decrease the greater the distance from it. The problem is that in the Sun, specifically in its atmosphere, the opposite occurs.
The Sun’s energy source is inside it, at the core, and can reach a temperature of 15 million degrees Celsius.
Image of the different layers that make up the Sun.
Moving away from the nucleus, but still in the solar interior, the temperature decreases until it reaches the solar surface, where its value is on average a little more than 5 thousand degrees Celsius.
So far everything is “normal” and behaves as expected. So the mystery: If we keep moving away from the surface of the Sun, one would expect the temperature to continue to decrease; but no, contrary to this, it begins to increase rapidly until it reaches more than a million degrees Celsius in a layer of the solar atmosphere called the corona.
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This is the famous problem of coronal heating, which, for decades, scientists have tried unsuccessfully to solve. But now an investigation led by a Colombian and published in the renowned magazine Nature might have the answer.
Image of a llama in the Sun captured by NASA’s Soho Observatory.
The study is titled Reconnection nanojets in the solar corona and its author is Patrick
Antolin Tobos. Born in Senegal, to a Colombian mother and French father, when he was young, Antolin traveled through various countries in Central and South America before entering to study physics and mathematics at the University of Los Andes.
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At the end of his undergraduate degree, Antolin traveled to the University of Kyoto (Japan) and the University of Oslo (Norway) to do a master’s and doctorate in astrophysics.
For the last 4 years, Antolín, who is now researching from the University of Northumbria (UK), He was given the task of trying to understand the problem of the solar corona from the observations of different space and ground telescopes.
As a result of his research, the scientist has proposed that the warming of the corona is due to a series of small, but numerous, explosions in the star’s atmosphere.
To these explosions, generated by the interactions of the Sun’s magnetic field, he named them nanojets.
According to Antolín, the Sun’s atmosphere is a place with a very low particle density, where atoms travel very far from each other, with almost no chance that they meet to transmit the energy. This density is even lower than what we can create in vacuum laboratories on Earth.
However, the solar magnetic field is very strong and causes the charged particles around it to interact to generate a series of magnetic loops of gas at very high temperatures, which are surely what many people have seen in photographs and videos. that telescopes have captured of the star.
Thanks to his research, Antolin was able to notice the heating mechanism of these loops and, in particular, the transformation of magnetic energy into thermal energy.
“The solar magnetic loops that make up the corona are anchored on the surface of the Sun, which is in constant motion. Resulting in a tangled magnetic cobweb of field lines”, Affirms Antolín.
And continues: “Sometimes, the threads of this web ‘unravel’, dissipating the energy they contain in the form of heat, and moving at high speed, forming flashes of light that we have called nanojets ”, says Antolín.
According to him, nanojets can be up to 500 kilometers wide and 1,500 kilometers long and last up to 10 seconds. In a span of 23 minutes, the scientists were able to identify up to 150 of them in a single heating episode of a solar loop. “
They might seem insignificant events when compared to the enormous size of the Sun. But they are not, because It turns out that each of these nanojets releases the energy equivalent to 2,000 Hiroshima bombs. “If they are the heating mechanism of the entire corona, nanojets would occur millions and millions of times simultaneously in the solar atmosphere,” says the expert.
On the shoulders of giants (human and robotic)
The history of the corona heating problem dates back to 150 years ago, when in a total solar eclipse a green spectral line was observed in the light that comes from the Sun using a technique called astronomical spectroscopy. accounted for the discovery of a supposed new element that did not correspond to any known on Earth, and to which it was called the coronium.
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It took several decades until in 1940 it was discovered that the element responsible for the emission was iron, superheated to such an extent that the temperature in the solar corona should be about 200 times higher than that of the surface of the star.
Since then, according to Antolin, dozens of hypotheses have been proposed trying to answer the coronal enigma, most of them based on two principles that, although they are different, are quite difficult to discern from each other.
It is, on the one hand, the so-called wave model and, on the other, the so-called magnetic reconnection —in which the nanojets proposed by the scientist are framed—, and which was proposed by the American astronomer Eugene Parker.
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At 92, Parker is one of the highest authorities in solar research, to the point that he is the only living person in whose honor NASA has named one of its space missions, the Parker Solar Probe, which is traveling to the Sun. to continue deciphering its mysteries.
According to Antolín, Parker assures in his model that the coronal loops are the “building blocks of the solar corona”, and that these are formed through a tangle of small magnetic reconnection processes between the braided power lines that are released releasing small amounts of heat.
But this had not been observationally proven. In order to do this, Antolin relied on costly analyzes of observations from maximum resolution telescopes capable of obtaining detailed images of the Sun such as the Atmospheric Imaging Assembly, the Solar Dynamics Observatory (SDO), the Interface Region Imaging Spectrograph ( Iris) and the Hinode / Solar Optical Telescope (SOT).
“We were lucky because we were able to coordinate the observations with these devices to study a region of the corona in the precise place and at the exact moment when a heating episode occurred accompanied by nanojets ”, says Antolin.
In addition to his study in Nature, Antolin published a brief review in ‘Detrás del paper’, a blog section of the same publisher in which the researchers tell how was the development of their study, from its conception to obtaining the results.
In this section, Antolin assures that his research was successful thanks to the fact that he ‘climbed on the shoulders of the giants’, alluding to a famous phrase by Isaac Newton, who referred to new knowledge in science is only possible thanks to the previous contributions of other scientists.
“Only, in this case, those giants were human (Parker) and robotic (the telescopes),” says Antolín.
The next step in this research will be to continue observing the Sun for more nanojets. For this, it will be essential to ‘stand’ again on the shoulders of the next robotic giants that will continue to study the Sun in the coming years, such as the Parker Solar Probe.
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