Most Powerful Cosmic Rays Ever Detected — Their Unknown Source Could Be Close to Earth

In a groundbreaking discovery, scientists have detected the most energetic cosmic rays ever observed, and they are coming from a mysterious source that could be remarkably close to Earth. These rays, composed of electrons and their antimatter counterparts, positrons, were observed at energy levels up to 40 teraelectronvolts (TeV)—a staggering 40,000 times the energy of visible light. This finding, reported in Physical Review Letters on November 25, 2023, challenges our understanding of the origins and behavior of high-energy particles in space.

Unraveling the Mystery of Cosmic Ray Sources

Cosmic rays, which are high-energy particles traveling through space, have long been a subject of fascination. They are produced by a variety of astrophysical phenomena, including supernova explosions, pulsars, and potentially unknown exotic sources. When these rays collide with Earth’s atmosphere, they create showers of secondary particles that can be detected on the surface. However, identifying their precise origin has always been a challenge, as these particles interact with magnetic fields and lose energy during their journey.

To study the cosmic ray electrons (CRe) at such high energy levels, researchers utilized the HESS observatory, a system of five 12-meter telescopes situated in the Khomas Highland of Namibia. Over a decade of observations, the telescopes scanned the atmosphere for signs of Cherenkov radiation, a faint blue glow caused by particles moving faster than light in the Earth’s atmosphere. By analyzing these signals, researchers were able to create an energy spectrum of the cosmic rays with unprecedented precision.

Kathrin Egberts, head of experimental astroparticle physics at the University of Potsdam in Germany, explained the implications of the findings: “This is an important result, as we can conclude that the measured CRe [cosmic ray electrons] most likely originate from very few sources in the vicinity of our own solar system, up to a maximum of a few thousand light years away, a very small distance compared to the size of our Galaxy.”

Further elaborating on the nature of these sources, Mathieu de Naurois, a researcher at the French National Centre for Scientific Research in Paris, added: “In the vicinity of our solar system, there [are] very efficient cosmic accelerators of electrons. Within a few hundred light-years, there are many stars, with the nearest ones typically lying two light-years from the Earth. We would therefore also expect to have a few ‘dead stars’ in this region, such as pulsars or supernova remnants, which could be the sources of these electrons.”

The Challenge to Current Models of Cosmic Ray Production

The fact that these cosmic ray electrons may come from sources so close to Earth raises intriguing possibilities about the types of astrophysical phenomena that could be responsible for such extreme particle acceleration. The sources of these high-energy cosmic rays could potentially be nearby pulsars, supernova remnants, or other exotic sources that have yet to be fully understood. One key aspect of these findings is that these cosmic rays seem to come from relatively few sources, implying that the processes involved in their production are rare or particularly energetic within a localized area.

In the words of Mathieu de Naurois, “The very low fluxes at larger TeV limit the possibilities of space-based missions to compete with this measurement.” This statement highlights the technical challenges of detecting such high-energy cosmic rays using space-based instruments, as the flux of these particles is incredibly low at the higher energy ranges. Despite the difficulties of detecting such rare events, HESS has proven capable of capturing these extraordinary particles, marking a significant achievement in cosmic ray research.

The Role of HESS in Unlocking the Cosmic Ray Mystery

The HESS system, which has been operational for over a decade, has been instrumental in capturing these high-energy cosmic rays. By observing the faint light produced by Cherenkov radiation, the HESS telescopes have provided valuable data that allows scientists to trace the paths and energies of these particles. The detailed data gathered by HESS is essential in helping researchers pinpoint the origins of these rays and understand the complex processes involved in their acceleration.

“H.E.S.S., in contrast, has a huge effective area, making it particularly suitable to study the high energy part of the electron spectrum,” de Naurois said. This advantage has allowed HESS to capture crucial data that further enhances our understanding of the cosmic ray phenomenon.

In addition to the data collected by HESS, other upcoming missions and observatories are expected to provide further insights into the high-energy phenomena that drive cosmic rays. The study’s findings are expected to serve as a critical benchmark for future research in high-energy astrophysics and may eventually lead to the identification of new, previously unknown sources of high-energy particles.

Implications for the Future of Astroparticle Physics

This discovery opens the door to an entirely new area of research in astroparticle physics. The study of cosmic rays at these unprecedented energy levels will undoubtedly shape future research in astrophysics, as scientists continue to explore the mysteries of high-energy radiation. The implications for understanding the energetic processes that govern the universe are profound, and this discovery has the potential to change the way we think about the forces shaping the cosmos.

“Our measurement does not only provide data in a crucial and previously unexplored energy range, impacting our understanding of the local neighbourhood, but it is also likely to remain a benchmark for the coming years,” said de Naurois.

As scientists continue to study these high-energy cosmic rays and their mysterious origins, the data collected by HESS will likely lead to new breakthroughs in our understanding of the universe’s most powerful phenomena. This discovery may also prompt further questions about the nature of cosmic rays and their role in the broader astrophysical landscape.