An international team of scientists has recorded the most powerful cosmic rays in the history of observations. The mysterious radiation sources are located relatively close to the Earth.
Scientists have recorded rays consisting of electrons and their antiparticles — positrons, with energies of up to 40 teraelectron volts (TeV), which is 40,000 times higher than the energy of visible light, reports Livescience.
The High Energy Stereoscopic System (HESS) Observatory in Namibia has detected these rays, which lose energy as they travel through space due to interaction with light and magnetic fields. This indicates that the sources of such energy must be relatively close, although what exactly gives rise to them — remains a mystery. Researchers published their findings on November 25 in the journal Physical Review Letters.
Katrin Egberts, head of the Department of Experimental Astrophysics at the University of Potsdam, explains that the cosmic ray electrons most likely come from several sources up to several thousand light-years away from the solar system. For comparison, the diameter of the Milky Way is approximately 100,000 light-years.
Cosmic rays are high-energy particles emitted by the Sun, supernova explosions, pulsars (rapidly rotating neutron stars), and other unknown objects. When the rays enter the upper layers of the Earth’s atmosphere, they break up into a shower of particles that reach the Earth’s surface. Reconstructing the original characteristics of the rays from these particles is a painstaking task with a high degree of uncertainty.
To detect the cosmic ray electrons, the team used the HESS Observatory — a complex of five 12-meter-high telescopes in the Homas Highlands of Namibia. For a decade, the telescopes have been scanning the upper atmosphere, looking for faint signs of Cherenkov radiation. Just as an airplane creates a sonic boom when it travels faster than sound, a particle emits a faint blue glow when it travels faster than light in a medium that slows it down.
Scientists have been detecting this glow and applying advanced algorithms to filter out the noise to create an unprecedentedly detailed energy spectrum of the rays that reach the Earth. The number of these rays decreases sharply at higher energy scales, so smaller space-based detectors are unlikely to be able to register them in sufficient numbers. However, the presence of particularly energetic particles has given scientists a clear understanding that at least some of the sources of the rays are close to our planet.
«The very low fluxes at higher TeV make it impossible for space missions to compete with this measurement, — notes Mathieu de Nourois, a researcher at the French National Center for Scientific Research in Paris. — Our measurements not only provide data in a crucial and previously unexplored energy range, influencing the understanding of the local environment, but are likely to remain a benchmark for years to come».
Source: Livescience
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