Astronomers puzzled by record-breaking energy radiation detected from the sun

 

Astronomers left astounded by the sun's highest-ever recorded energy radiation, as a recent discovery raises intriguing questions about the mechanisms behind such emissions from its solar atmosphere.

Since the 1990s, scientists have observed various forms of high-energy radiation, including gamma rays, emanating from the sun, as predicted by theoretical models.

However, a groundbreaking study, published in the journal Physical Review Letters on Thursday, unveils new findings based on six years of data, indicating a significantly higher level of gamma rays from the sun than previously anticipated.

"The sun holds more surprises than we ever imagined. We believed we had a thorough understanding of this star, but it seems that's not the case," stated co-author Mehr Un Nisa from Michigan State University (MSU).

Although this radiation does not reach the Earth's surface, it leaves distinct "telltale signatures" observable in the atmosphere.

Scientists achieved this groundbreaking observation through their work at the High-Altitude Water Cherenkov Observatory (HAWC), situated on the slopes of the Sierra Negra volcano near Puebla, Mexico, at an altitude of approximately 4,100 meters (13,500 feet).

Unlike conventional telescopes, this unique facility is purpose-built to detect gamma rays and cosmic rays originating from the most extreme environments in the universe, such as supernova explosions.

HAWC utilizes a network of 300 large water tanks, each containing roughly 200 metric tons of water, strategically positioned between two dormant volcano peaks in Mexico.

At the HAWC facility, scientists observe the aftermath of gamma rays colliding with air in the atmosphere, resulting in the formation of "air showers," which are essentially particle explosions invisible to the human eye.

During these interactions, the energy of the gamma rays is transformed into particle fragments and light, which are then detected and observed by the HAWC team.

The High Altitude Water Cherenkov Observatory (HAWC), located in central Mexico, is actively collecting data on high-energy gamma rays as they interact with the Earth's atmosphere. (Credit: Ignacio Taboada).

By analyzing data collected from these interactions since 2015, Dr. Nisa and her team had accumulated sufficient information by 2021 to conduct a detailed examination of the sun's gamma rays.

The sun is known to emit energy across various wavelengths, with some being more prevalent than others. One of these wavelengths is visible light, carrying an energy of about 1 electron volt. In contrast, the gamma rays observed by Dr. Nisa and her team had energy levels around 1 trillion electron volts, equivalent to 1 tera electron volt (1 TeV). The researchers were not only surprised by this remarkably high energy level but also by the significant quantity of these rays that they were detecting.

"When we first saw this excess of gamma rays in the data collected over six years, we thought we must have made an error. The sun cannot possibly emit such intense radiation at these energies," said the physicist, who will soon join MSU's faculty.

As early as the 1990s, scientists had theorized that the sun might produce gamma rays through interactions with cosmic rays from sources like black holes or supernovas colliding with protons in the sun. However, it was believed to be extremely rare for these gamma rays to reach Earth, and at that time, there were no instruments capable of detecting such high-energy gamma rays.

In 2011, NASA's Fermi Gamma-ray Space Telescope made the first observation of gamma rays with energies exceeding a billion electron volts. However, its measurements of the sun's gamma rays were limited to around 200 billion electron volts.

The recent observation marks the first time scientists have demonstrated that the sun's gamma rays can extend into the TeV range, reaching nearly 10 TeV, which may be the upper limit, as suggested by Dr. Nisa.

Despite this groundbreaking discovery, researchers are still uncertain about the precise mechanisms responsible for generating such high-energy gamma rays from the sun. The role of the sun's magnetic fields in this phenomenon remains elusive and requires further investigation.