Unprecedented Discovery: Most Energetic Solar Light Ever Observed Confounds Scientific Community

Scientists have uncovered the most intense light ever seen originating from the sun, specifically in the form of gamma rays. This revelation, based on an analysis of six years of collected data, upends prior scientific beliefs and provokes new questions about the inner workings and magnetic properties of the sun.

A team of physicists have identified an unparalleled level of energetic light issuing from the sun.

As it turns out, some of the universe’s greatest enigmas are often hidden in plain sight—take the sun as an example.

Mehr Un Nisa, a postdoctoral researcher soon to join the faculty at Michigan State University, states, “Our previous assumptions about the sun have been significantly disrupted.” Nisa is the lead author of a recently published paper in the journal Physical Review Letters that discusses the groundbreaking discovery of this exceptional solar light.

The international consortium responsible for this discovery additionally noted that these gamma rays are astonishingly luminous—far more so than previously thought possible.

A New Perspective Through HAWC

While these high-energy gamma rays do not make it to the Earth’s surface, their presence is indicated through specific markers. These markers were identified by Nisa and her team, who utilized the High-Altitude Water Cherenkov Observatory, commonly known as HAWC.

Supported by the National Science Foundation and the National Council of Humanities Science and Technology, HAWC plays a crucial role in this investigation. Unique among observatories, HAWC operates continuously, day and night.

Nisa, who is affiliated with the Department of Physics and Astronomy in the College of Natural Science, remarks, “Our observational capabilities have evolved significantly in recent years. Our facility operates around the clock, unlike other ground-based telescopes that can only observe the sun at nighttime.”

In contrast to traditional telescopes, HAWC employs an array of 300 large water tanks, each containing approximately 200 metric tons of water. This setup is situated between two inactive volcanic peaks in Mexico at an altitude exceeding 13,000 feet.

From this elevated location, the observatory can detect the aftermath of gamma rays interacting with Earth’s atmosphere. These interactions lead to the formation of phenomena known as air showers, which are akin to undetectable explosions of particles.

The energy initially held in the gamma ray is dispersed into new, lower-energy particles and light during this process. It is these particles—and their subsequent derivatives—that HAWC is equipped to detect.

When these particles come into contact with the water within HAWC’s tanks, a specific form of radiation known as Cherenkov radiation is produced. This radiation can be observed through HAWC’s advanced instrumentation.

Nisa and her team commenced data collection in 2015. By 2021, they had amassed sufficient data to scrutinize the sun’s gamma rays in great detail.

“Upon analyzing six years of data, we discovered an unexpected abundance of gamma rays,” says Nisa. “Our initial reaction was disbelief; we couldn’t imagine the sun emitting light at such high energies.”

Shattering Previous Theories

Historically, the sun emits light at various energy levels, with some types being more prevalent. For instance, its nuclear reactions primarily produce visible light, carrying an energy of about 1 electron volt.

In contrast, the gamma rays observed by Nisa and her colleagues had energies close to 1 trillion electron volts, abbreviated as 1 TeV. Not only was this energy scale startling, but the sheer quantity of these rays was also surprising.

Earlier hypotheses from the 1990s postulated that the sun could emit gamma rays when cosmic rays—particles accelerated by celestial phenomena like black holes or supernovae—collide with the sun’s protons. However, these theories also suggested that such gamma rays would seldom be detectable from Earth.

Recent technology has finally made the detection of such high-energy gamma rays possible. NASA’s Fermi Gamma-ray Space Telescope, launched in 2011, initially identified gamma rays in the range of more than a billion electron volts.

Over subsequent years, the Fermi mission demonstrated that these rays could be highly energetic and occur in greater numbers than initially forecasted. The limitations of space-based telescopes like Fermi prompted terrestrial observatories like HAWC to investigate further.

The HAWC collaboration, representing more than 30 institutions worldwide, has now demonstrated for the first time that the sun’s rays extend up to nearly 10 TeV, which seems to be the upper limit, according to Nisa.

This groundbreaking discovery raises more questions than it provides answers. Scientists specializing in solar studies will now focus on understanding how these gamma rays achieve such extraordinary energy levels and what role the sun’s magnetic fields play in this process.

For those in the field of astrophysics, the enduring intrigue lies in the mysteries yet to be solved. This recent discovery signifies that our current understanding of the sun, our closest star, is far from complete.

“It demonstrates that HAWC is expanding our comprehension of the universe at the highest energy levels, while simultaneously compelling us to reevaluate our assumptions about our very own sun,” concludes Nisa.

Reference: “Discovery of Gamma Rays from the Quiescent Sun with HAWC” by A. Albert et al. (HAWC Collaboration), published on 3 August 2023 in Physical Review Letters.
DOI: 10.1103/PhysRevLett.131.051201

Frequently Asked Questions (FAQs) about gamma rays

More about gamma rays

• Physical Review Letters Journal
• High-Altitude Water Cherenkov Observatory (HAWC)
• National Science Foundation
• Michigan State University Department of Physics and Astronomy
• NASA’s Fermi Gamma-ray Space Telescope
• Ohio State University Physics Professors