When Shah Bahauddin was deciding what to research for his PhD, he had no intention of getting entangled in one of the most macabre problems in astrophysics: why the Sun’s distant atmosphere is so hot above the surface The
The minor theme of his choice was a short and brief loop of solar light, barely detectable given the Sun’s grand plan.
But size is not everything. As it turns out, astronomers had been looking for such a small explosion for more than half a century.
Flickering just below the sun’s super-hot corona, the thunderous Bahauddin may very well be the first complete glimpse of the solar ‘nanoflare’ – from its bright beginnings to its inevitable sealing demise. And we could easily remember it.
If subtle and transitory loops are such an affair, it can help explain how the Sun’s corona became hundreds of times warmer than its visible surface – a mystery known as the coronal heating problem.
“I felt that the loops probably warmed up the surrounding environment a bit,” Bahauddin admits.
“I never thought it would make so much energy that it could actually circulate hot plasma to the corona and heat it.”
A billion times smaller than regular solar flares, nanofluors are incredibly difficult to spot and exist only in theory, so researchers are still reluctant to call the discovery by that official name.
In theory, we have an idea of what a nanoflare should look like, but it is based on several assumptions.
“Nobody really knows because no one has seen it before,” Bahauddin says. “It’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 eruptions might look like in reality.
If they really exist, they are almost impossible, which happens millions of times without our devices being seen millions of times. Although our technology is getting better.
For example, in 2017, our best glimpse of a nanoflayer came from the absence of a large person. An active region in the Sun, which hosted very few normal-sized flares, showed a warm level. Some of the overlooks were obviously the contribution of energy to the atmosphere. A nanoflare suited the case.
Technically, a proper nanoflayer is thought to have caused an explosion of heat by the Sun’s tricky magnetic fields, which are produced by bubbling plasma bubbles below.
When these areas are reunited, they are thought to be the cause of the explosive process – equivalent to about 10 billion tons of TNT. It activates and accelerates nearby particles, and if all this activity is strong enough to heat the sun’s corona, thousands of kilometers up, it is called a nanoflare.
up: Close-up of one of the studied loop brightening. Each inset frame zooms forward (left to right), showing the potent nanoflare.
Analyzing some of the best images of the Sun’s corona taken from NASA’s interface field imaging spectrograph, or IRIS satellite, the new discovery ticks both of those boxes.
Not only this, it was a small loop of light millions of degrees higher than its surroundings, the way it exploded seemed curious.
“You have to check if the energy from the nanofare can go to the corona,” Bahauddin explains.
“If the energy goes elsewhere, it does not solve the coronal heating problem.”
Looking at the figures, it appeared that heavier elements such as silicon became much warmer and more energetic than lighter elements such as oxygen, which is contrary to what you expected.
Discovering a type of heat that could affect the oxygen atom differently in a different way, the researchers found only one match: a magnetic recombination event.
In these complex chaotic situations, heavy ions have an advantage, as they can resolve through a multitude of light ions and steal all the energy, creating a lot of heat in the process.
But it was only a hypothesis, and it seemed like a long shot. The correct ratio of silicon to oxygen is required in the conditions required to achieve this type of heat. Can it really exist?
“So we looked at the measurements, and saw that the numbers exactly matched,” Bahauddin explains.
To the team’s amazement, it appeared that they had stumbled upon an actual explanation for coronal heating. The next step was to see if it really heats the corona.
Analyzing data from the area just above the luminous loop, the team discovered their final clue before it flared up.
“And there was just a 20-second delay,” Bahauddin recalls. “We looked at the brightening, and then we suddenly saw that the corona super-heated at multi-million degree temperatures.”
Already, the team has detected nine other ridges on the surface of the Sun that also show a transfer of energy similar to the corona.
Whether this localized heating is sufficient to explain the high temperatures found across the Sun’s corona will depend on how many other ends astronomers can discover.
If their frequency and location are often and widely enough, these bursts of energy may at least partially answer the mystery surrounding coronal heating.
Yet in all likelihood, astronomers find that the play possibly has many invisible mechanisms. This is probably not the only thing warming the sun’s atmosphere to such blistering temperatures, and many of the ideas we have are no longer mutually exclusive.
Other theories include electromagnetic waves emanating from the Sun, heating particles and allowing the outer atmosphere to ‘surf’.
This small loop is just a small piece of the puzzle.
The study was published in Nature astronomy.