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, in the core, which can reach a temperature of 15 million degrees Celsius.
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, just over 5,000 degrees Celsius.
So far everything is “normal” and behaves as expected. So the mystery: If we continue to move 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 coronal heating problem, still unsolved.
For decades, scientists have tried unsuccessfully to respond to this phenomenon. But now an investigation led by a Colombian and published in the renowned magazine Nature might have the answer.
Its 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 to various countries in Central and South America before entering to study physics and mathematics at the Universidad de los Andes.
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At the end of his undergraduate studies, Antolin traveled to the University of Kyoto (Japan) and the University of Oslo (Norway) to do a master’s and doctorate in astrophysics.
During the last 4 years, Antolín, who is now researching from the University of Northumbria (United Kingdom), undertook 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, Antolín has proposed that the warming of the corona is due to a series of small, but numerous, explosions in the star’s atmosphere. The scientist called these explosions, generated by the interactions of the Sun’s magnetic field, nanojets.
“The Sun, like the Earth, has a magnetic field that makes the charged particles around it interact, but it 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 ”, says Antolín.
However, in the case of the Sun, unlike the Earth, the magnetic field is very strong, so much so that it generates a series of magnetic loops of gas at a very high temperature and that many people have surely seen in the photographs and videos of the Sun taken by telescopes.
Thanks to his research, he was able to notice the heating mechanism of solar 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. What results is a tangle of field lines like a very complicated magnetic cobweb, ”says Antolín.
And he continues: “Sometimes, the threads of these magnetic cobwebs ‘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. These 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, we were able to identify up to 150 of them in a single solar loop heating episode. “
They might seem like insignificant events when compared to the enormous size of the Sun. “But this is not the case, 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, these 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 a total solar eclipse was observed using a technique called astronomical spectroscopy, a green spectral line in the light that came from the Sun that gave account of 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 processes of magnetic reconnection between the braided energy lines that are they release releasing small amounts of heat.
But this had not been observationally proven. In order to do this, Antolín relied on costly analysis 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 had some luck because we were able to coordinate the observations with these devices to observe a region of the corona in the right place and at the exact moment when a heating episode accompanied by nanojets occurred,” says Antolin.
In addition to his study in Nature, Antolín published a brief review in ‘Behind the’ paper ” a section of blogs from the same publisher in which the researchers tell how the development of their study was, from its conception to the obtaining of the results.
In this section, Antolin assures that his research would not have been successful without having ‘climbed on the shoulders of the giants’, alluding to a famous phrase by Isaac Newton, who referred to the fact that 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, according to Antolin, will be to continue observing the Sun in search of nanojets. For this, it will be essential to ‘stand’ again on the shoulders of the next robotic giants that will study the Sun in the coming years, such as the Parker Solar Probe.
NICOLÁS BUSTAMANTE HERNÁNDEZ