After more than a decade of rigorous observation, scientists at the High Energy Stereoscopic System (HESS) observatory in Namibia have detected the most energetic cosmic electrons ever recorded, with energies reaching up to 40 teraelectronvolts (TeV). This groundbreaking discovery opens new pathways to understanding the universe’s most extreme environments.
What Are Cosmic Rays?
Cosmic rays are high-energy particles originating from powerful cosmic events, including supernovae, pulsars, black holes, and other energetic phenomena. Discovered in 1912 by Austrian physicist Victor Hess during balloon ascents to measure ionizing radiation, these particles include protons, atomic nuclei, and electrons. Among these, cosmic-ray electrons (CRe) and positrons (their antimatter counterparts) are particularly rare and challenging to detect due to energy loss during their journey through space, where they interact with light and magnetic fields.
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The detection of these high-energy electrons and positrons is crucial for unveiling the workings of cosmic particle accelerators. These accelerators, located in our galactic neighborhood, produce particles with energies far exceeding those generated by human-made accelerators like the Large Hadron Collider.
Why Is This Discovery Significant?
The electrons detected by HESS are the most energetic ever observed, marking a breakthrough in astrophysics. The detection of these particles provides compelling evidence of violent cosmic processes that unleash extraordinary amounts of energy. “These findings reveal powerful particle accelerators in the universe, often linked to dramatic events such as stellar explosions, neutron stars, pulsars, or even black holes,” explained Mathieu de Naurois, deputy director of the HESS collaboration.
The rapid energy loss of electrons at these levels indicates that their sources are relatively close to Earth, within a few thousand light-years—a tiny distance compared to the Milky Way’s 100,000 light-year diameter. Researchers suggest possible sources include aging supernova remnants, pulsars, or Wolf-Rayet stars, though their exact origins remain uncertain.
How HESS Made the Discovery
The HESS observatory, an array of five telescopes in Namibia, detects Cherenkov radiation—a faint blue glow created when high-energy particles strike Earth’s atmosphere at speeds exceeding that of light in the medium. Over ten years, HESS telescopes collected massive amounts of data, using sophisticated algorithms to sift through cosmic noise and isolate the electron signatures.
This meticulous approach allowed researchers to extend the cosmic electron energy spectrum to an unprecedented 40 TeV, identifying a sharp “break” at around 1 TeV. This energy limit indicates that the particles lose energy quickly, reinforcing the idea that their sources are nearby.
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Detecting these rare particles is no small feat. Space-based instruments, with their small detection areas, struggle to capture enough high-energy electrons. Ground-based systems like HESS offer larger effective areas but must overcome challenges of separating electrons from the heavier cosmic-ray protons and nuclei. The advanced algorithms used in this study achieved unprecedented accuracy, setting a benchmark for future research. “This measurement provides critical data in an unexplored energy range and is likely to remain a reference for years,” de Naurois said.