Scientists detect 'highest

Jul 03, 2023

Mehr Un Nisa

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The recent discovery of the highest-energy light coming from the Sun has perplexed scientists.

The new discovery is based on six years of data evaluated by Michigan State University researchers.

This type of light, known as gamma rays, detected from the Sun is far brighter than scientists had predicted.

“The sun is more surprising than we knew. We thought we had this star figured out, but that’s not the case,” said Mehr Un Nisa, study co-author, in an official release.

The Sun emits energy in several wavelengths, one of which is visible light that carries around one electron volt of energy.

Since the 1990s, scientists have speculated that gamma rays might be produced by the Sun when high-energy cosmic rays from a black hole or supernova collide with its protons. However, scientists hypothesized that it would be extremely rare for these gamma rays to reach Earth.

Surprisingly, Nisa and her colleagues discovered gamma rays with an unusually high energy of one trillion electron volts, or one tera electron volt (in short, 1 TeV).

“After looking at six years’ worth of data, out popped this excess of gamma rays. When we first saw it, we were like; we definitely messed this up. The Sun cannot be this bright at these energies,” said Nisa.

In 2011, the arrival of NASA's Fermi Gamma-ray Space Telescope resulted in the first observation of gamma rays with enormous energy of more than a billion electron volts.

Fermi’s measurement of the Sun’s gamma rays estimated the maximum energy to be around 200 billion electron volts.

The new study showcases that the gamma-ray energy could far exceed this figure. In fact, it could extend maximum into the TeV range – up to roughly 10 TeV.

However, scientists are still uncertain how these gamma rays acquire such extraordinarily high energy.

Jordan A. Goodman/Wikimedia Commons

According to the authors, gamma rays leave behind "telltale signatures" that may be seen in the atmosphere.

A specialist High-Altitude Water Cherenkov Observatory, or HAWC, identified this signal.

HAWC is unlike the conventional telescope. It employs a network of 300 colossal water tanks, each holding around 200 metric tons of water. The network is located in Mexico, more than 13,000 feet above sea level, between two dormant volcanic summits.

“From this vantage point, it can observe the aftermath of gamma rays striking air in the atmosphere. Such collisions create what are called air showers, which are a bit like particle explosions that are imperceptible to the naked eye,” explained the release.

When shower particles reach the water in HAWC's tanks, they produce what is known as Cherenkov radiation, which may be detected using the observatory's equipment.

“Currently, the discovery creates more questions than answers. Solar scientists will now scratch their heads over how exactly these gamma rays achieve such high energies and what role the sun’s magnetic fields play in this phenomenon,” they concluded.

The study was published in the journal Physical Review Letters.

Study abstract:

We report the first detection of a TeV γ-ray flux from the solar disk (6.3σ), based on 6.1 years of data from the High Altitude Water Cherenkov (HAWC) observatory. The 0.5–2.6 TeV spectrum is well fit by a power law, dN/dE=A(E/1  TeV)−γ, with A=(1.6±0.3)×10−12  TeV−1 cm−2 s−1 and γ=3.62±0.14. The flux shows a strong indication of anticorrelation with solar activity. These results extend the bright, hard GeV emission from the disk observed with Fermi-LAT, seemingly due to hadronic Galactic cosmic rays showering on nuclei in the solar atmosphere. However, current theoretical models are unable to explain the details of how solar magnetic fields shape these interactions. HAWC’s TeV detection thus deepens the mysteries of the solar-disk emission.