When Shah Bahauddin was deciding to do research for a PhD, he did not intend to get involved in one of the most worrying problems of astrophysics: why is the Sun’s distant atmosphere hotter than its surface?
The simplest subject of their choice was a small and concise loop of solar light, which could hardly be detected given the magnificent scheme of the sun.
But size is not everything. As it turned out, astronomers have been searching for small explosions like this for more than half a century.
Shining just below the sun’s super-hot corona, Bahauddin’s stunned explosion may be the first complete glimpse of the solar ‘nanoflare’ – from its sudden bright start to its inevitable sizzling death. And we would have missed it so easily.
If subtle and transient loops like this are frequently related, it could help explain how the sun’s coron got hundreds of times hotter than its visible surface – a mystery known as the fundamental heating problem.
“I thought maybe the loops warmed up the atmosphere a little bit,” Bahauddin admits.
“I never thought it would generate so much energy that it could actually run hot plasma into the corona and heat it up.”
Loop brightenings observed. (Bahauddin et al., Nature Astronomy, 2020)
Billions of times smaller than regular solar flares, nanoflares are incredibly difficult to find and only exist in theory, so researchers are still reluctant to call them discoveries by official name.
In theory, we have an idea of what a nanoflare should look like, but it is based on many assumptions.
“Really no one knows because no one has seen this before,” says Bahauddin. “That’s an educated guess, let’s say.”
Ever since astrophysicist Eugene Parker first proposed the idea of nanoflares in the 1970s, experts have been trying to figure out what these explosions look like in reality.
If it really did exist, it would be almost impossible to see, regardless of our instrument, occur millions of times a second. Yet our technology is getting better.
In 2017, for example, our best glimpse of the nanoflare came from the absence of a large. The active region in the sun, which hosted very few normal-sized flames, showed a strange level of heating. Something invisible clearly had to contribute to the release of energy into the atmosphere. Nanoflare suits the case.
Technically, in order to be considered a suitable nanoflare, heat must be dissipated by the sun’s entangled magnetic fields, which are produced by churning plasma bubbles.
When these fields reconnect, they are thought to be the cause of the explosive process – about 10 billion tons of TNT. Equivalent of. This excites and accelerates the surrounding particles, and if all that activity is strong enough to heat the sun’s corona, thousands of kilometers above, it is called a nanoflare.
(NASA / SDO / IRIS / Bahauddin)
Above: A close study of one of the loop bright brings. Each inset frame zooms forward (left to right), showing the pagan nanoflare.
An analysis of some of the best images of the Sun’s corona taken from NASA’s Interface Region Imaging Spectrograph or IRIS satellite, the new discovery ticks both.
This tiny loop of light wasn’t as hot as millions of degrees around it, the way it exploded seemed strange.
Bahauddin explains, “You have to check whether the energy from the nanoflare can be dispersed into the razor corona.”
“If the energy goes elsewhere, it doesn’t solve the coronal heating problem.”
Looking at the data, it seems that heavier elements like silicon have become warmer and more powerful than lighter elements like oxygen, which is exactly the opposite of what you would expect.
In the search for the type of heat that can affect a heat oxygen atom differently from a silicon atom, the researchers found only one match: the occurrence of a magnetic recombination.
In these complex chaotic circumstances, heavy ions have an advantage, as they can plow through the congestion of lighter ions and steal all the energy, which receives extreme heat in the process.
But that was just a hypothesis, and it felt like a long shot. Only the right amount of silicon in silicon is required for the conditions required to achieve this type of heating. Does it really exist?
“So we went back to the measurement, and saw that the numbers matched exactly.” Bahauddin explains.
To the surprise of the team, it looked like they had stumbled upon a real revelation of coronal heating. The next step was to see if it really warmed the corona.
Analyzing the data from the region above the bright loop, before it explodes, the team finds their final key.
Bahauddin recalls, “And there was only a 20-second delay.” We looked bright, and then we suddenly saw that the corona had become extremely hot at a multi-million degree temperature. “
Already, the team has found nine other loops on the surface of the sun that also show a similar transfer of energy rays into the corona.
Whether this local heating is sufficient to explain the high temperatures seen in the sun’s corona will depend on how many loops astronomers can detect.
If their frequencies and locations are frequent and sufficiently extensive, these energy eruptions may at least partially answer the mystery surrounding coronal heating.
Yet in all likelihood, astronomers think that there are probably many invisible mechanisms at play. It’s probably not the only thing that heats the sun’s atmosphere to such ambiguous temperatures, and many of the ideas we now have aren’t mutually exclusive.
Other theories include electromagnetic waves washing out of the sun, allowing particles to heat up and allow them to ‘surf’ into the external atmosphere.
This small loop is a small part of the puzzle.
The study was published in Nature astronomy.
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