Bengaluru, Jul 24 (PTI) Scientists from the Indian Institute of Astrophysics (IIA) in Bengaluru have managed to peek into one of the fleeting windows to the Sun — miniature plasma loops in the lower layers of the Sun’s atmosphere — securing another piece of clue that helps in understanding its mysteries better.
The “breakthrough” reveals the dazzling world of miniature plasma loops, or tiny loops, which stretch almost as long as the distance between Kashmir and Kanyakumari, Tanmoy Samanta, a faculty member at IIA and a co-author of the study, told PTI.
His colleague and co-author Jayant Joshi said IIA’s work has led to substantial progress in the study of miniature plasma loops.
“About half-a-decade ago, scientists discovered the existence of miniature plasma loops. But, unlike coronal loops, which are large and therefore can be observed with small telescopes, accessing tiny loops is not easy,” Joshi told PTI.
Among the most intriguing features of the Sun’s outer layer are coronal loops, arc-like beautiful structures of hot plasma that glow at a temperature over a million degrees, Samanta said.
“And these large loops in the solar corona, or outer atmosphere, have long been studied by scientists,” he added.
According to Joshi, the sighting of their miniature counterparts has not been consistent as ground-based telescopes are limited and depend on sky conditions.
“IIA’s latest work offers a little more depth to our understanding of tiny loops,” he added.
Annu Bura, who is pursuing her PhD at IIA and the first author of the paper published on the result, said she started the project to build the skills necessary for her future research.
“I was new to the field and wanted to understand how to work with observational data, particularly using both ground-based and space-based instruments. It was my first project, and I saw it as a way to get hands-on experience with real solar data,” Bura told PTI.
It was also part of her broader PhD objective, she said.
“I wanted to study the dynamics of small-scale explosive features in the solar atmosphere using high-resolution observations,” she added.
While exploring data from the Goode Solar Telescope at the Big Bear Solar Observatory (BBSO) in the USA — a ground-based telescope known for its excellent spatial resolution, Bura said they came across a very bright loop in the H-alpha line.
The H-alpha spectral line from Hydrogen atoms, added Bura, is a key line for probing the solar chromosphere, which is just above the visible surface of the Sun.
The team found that in the redder or longer wavelength part of this line, these loops appear as bright, delicate arcs similar to coronal loops and these were seen very clearly for the first time.
“Such a clearly visible loop in H-alpha is quite unusual, which immediately caught our attention,” she added.
To understand the structure better, Bura said she searched for coordinated observations from space-based instruments.
“We found coordinated data from the Solar Dynamics Observatory (SDO) and the Interface Region Imaging Spectrograph (IRIS) both NASA missions focused on studying the Sun,” she added.
With the availability of this multi-instrument, multi-wavelength coverage, it became possible for the team to study the loop in much greater detail, across different layers of the solar atmosphere.
“Our multi-instrument observation allowed us to analyse the loops not only in visible light but also in ultraviolet and extreme-ultraviolet wavelength, revealing their behaviour across the chromosphere, transition region and corona, the different layers of the Sun’s atmosphere,” said Bura.
They also found that although these tiny loops can be about 3,000 km to 4,000 km long, they have a width of less than 100 km.
“And these tiny loops live fast and die young, lasting only a few minutes, making it extremely difficult to observe them and interpret their physical origins,” added Bura.
However, Bura said these loops punch above their weight when it comes to understanding the Sun.
“They offer a new window into how magnetic energy is stored and released in the solar atmosphere on small scales,” she pointed out.
The study also unearthed “mysteries” providing fodder for future research.
For instance, when they studied the plasma temperature inside these loops, it was found to be soaring above several million degrees — hot enough to shine in the extreme ultraviolet, visible in SDO’s Atmospheric Imaging Assembly.
“This behaviour is puzzling as the loops have a height of around 1 million metres and lie within the chromosphere, where plasma densities are much higher than the corona. It is quite difficult to heat the plasma to such a hot temperature,” said Joshi.
He added, “future spectroscopic observation can help us to understand this puzzling behaviour.” Future telescopes with even sharper chromospheric imagers and more sensitive magnetic field measurements — such as India’s proposed 2-meter aperture National Large Solar Telescope (NLST), planned near Pangong Lake in Ladakh — could help unlock even more secrets hidden within these small-scale solar features, the team conclude in their study.
The study was published in ‘The Astrophysical Journal’. PTI JR KH
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