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Sun’s gamma rays shine brighter than expected

In an astonishing revelation, the sun has proven to be even more enigmatic than we thought. According to Mehr Un Nisa, a postdoctoral research associate at Michigan State University, and corresponding author of a groundbreaking paper in Physical Review Letters, the sun has showcased the highest-energy light ever detected. This remarkable light, called gamma rays, has turned out to be far brighter than anticipated, leaving scientists baffled by its abundance.

The international team responsible for this discovery has unveiled a whole new facet of our closest star, challenging our existing understanding of its nature. As Nisa prepares to join MSU's faculty, the scientific community eagerly awaits further insights into this captivating .

Watching like a HAWC

Within the vast expanse of space, the sun has kept hidden secrets, brought to light by the diligent work of Mehr Un Nisa and her colleagues at the High-Altitude Water Cherenkov Observatory (HAWC). This exceptional observatory stands apart from conventional telescopes, employing a unique network of 300 large water tanks to capture elusive gamma rays' signatures. Nestled between dormant volcano peaks in Mexico at an altitude of over 13,000 feet, HAWC operates non-stop, enabling observation of air showers created when gamma rays collide with Earth's atmosphere.

The collisions lead to explosions called air showers, invisible to the naked eye, but not to HAWC's instruments. As the shower particles interact with the observatory's water tanks, they produce detectable Cherenkov radiation. This groundbreaking approach allowed Nisa and her team to amass data since 2015, and in 2021, they made a surprising revelation: an abundance of gamma rays emanating from the sun at energies previously unimaginable.

Initially skeptical, the team confirmed this phenomenon through meticulous analysis, realizing that the sun holds more energy secrets than we ever thought possible. With HAWC's constant watchfulness, the sun's mysteries continue to unfold, challenging our understanding of our celestial neighbor.

What an excess of solar gamma rays looks like to the High-Altitude Water Cherenkov Observatory Collaboration, which includes researchers from Michigan State University. Credit: HAWC Collaboration

Making history

The sun's luminous radiance encompasses a wide spectrum of energies, with some more prevalent than others. While the sun emits copious visible light with an energy of around 1 electron volt, it surprised scientists by producing gamma rays with a whopping 1 tera electron volt (1 TeV) – a trillion times more energetic. In the 1990s, researchers theorized that high-energy cosmic rays smashing into the sun's protons could generate gamma rays. However, detecting them remained a challenge until NASA's Fermi Gamma-ray Space Telescope observed gamma rays above a billion electron volts in 2011.

The Fermi mission revealed not only the immense energy of these gamma rays but also their abundance, surpassing scientists' initial expectations. As Fermi's detectors had limits, theorists at Ohio State University encouraged the HAWC Collaboration, representing over 30 institutions worldwide, to investigate further. This collaborative effort, with contributions from Michigan State University, unveiled the sun's gamma rays extending into the TeV range, nearly 10 TeV being the maximum observed.

This groundbreaking discovery leaves solar scientists with new questions about how the sun achieves such high energies and the role of its magnetic fields in this phenomenon. Nevertheless, it adds to our understanding of our 's mysteries and illuminates a different perspective on our nearest star, sparking excitement and curiosity among researchers. Indeed, the sun continues to surprise us, shedding light on previously unexplored realms of the cosmos.

Source: Michigan State University

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