Une source de particules extrêmement énergétiques dans la Voie Lactée identifiée

A source of extremely high-energy particles in the Milky Way has been identified, marking a significant step forward in understanding cosmic-ray acceleration processes. Researchers using data from multiple observatories confirmed that the celestial object known as LHAASO J1912+1014u functions as a proton PeVatron, a cosmic particle accelerator capable of producing protons with energies exceeding one quadrillion electron volts (PeV). The discovery, based on observations from NASA’s Fermi Gamma-ray Space Telescope and other instruments, confirms the existence of such a powerful source within our galaxy. The identification of LHAASO J1912+1014u came after years of analysis involving data from several key projects. These include the Tibet AS gamma experiment, initiated by Japan and China in 1990, and China's Large High Altitude Air Shower Observatory (LHAASO), both of which have recorded numerous gamma-ray sources above 0.1 PeV. Among these, LHAASO J1912+1014u stood out due to its unusually high-energy emissions. Located in the constellation Aquila, near the bright star Altair, the object was initially thought to be a supernova remnant. However, the detection of emissions above 100 teraelectron volts (TeV) suggested a different origin. Cosmic rays, predominantly composed of protons with some electrons, can achieve energies far beyond what human-made accelerators can generate. The Large Hadron Collider, for instance, accelerates protons to nearly the speed of light, yet these energies remain dwarfed by the cosmic rays observed in deep space. Understanding how such extreme energies are achieved in nature is crucial for unraveling the mechanisms behind high-energy phenomena in the universe. Tsunefumi Mizuno, associate professor at Hiroshima University's Hiroshima Astrophysical Science Center and lead researcher of the study, emphasized the significance of identifying a proton PeVatron. “This immense energy makes cosmic rays important in astronomy and astrophysics,” he said. Cosmic rays are measured in electron volts, the energy gained by an electron moving through an electric potential difference of one volt. The highest energies observed in galactic cosmic rays surpass 1 quadrillion electron volts, making them a subject of intense interest among astrophysicists. Confirming LHAASO J1912+1014u as a proton PeVatron required data from multiple observatories. In addition to the Tibet AS gamma and LHAASO experiments, the Fermi Large Area Telescope (Fermi-LAT), operated by NASA with contributions from Hiroshima University, played a critical role. The FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope (FUGIN), led by Japan, and the Chandra X-ray Observatory, managed by NASA, also provided essential information. Together, these instruments offered a comprehensive view of the object across various wavelengths. Mizuno explained that previous attempts to identify proton PeVatrons faced challenges. While the Tibet AS gamma and LHAASO experiments detected sub-PeV gamma-ray sources, their limited resolution made it difficult to distinguish between protons and electrons as the primary source of these emissions. Proton PeVatrons are particularly valuable because they indicate regions where protons, rather than electrons, are being accelerated to extreme energies, offering insights into the physics of such environments. With the combined data, researchers were able to analyze LHAASO J1912+1014u in greater detail. They found that the source is not just a point-like object but an extended structure spanning more than one degree in angular size. To put this into perspective, the apparent size of the Moon in the sky is roughly half a degree, meaning this source appears significantly larger. Such an extensive emission region suggests complex interactions occurring within the system. The confirmation of LHAASO J1912+1014u as a proton PeVatron opens new avenues for studying cosmic-ray production mechanisms. Scientists will continue analyzing data from existing observatories and planning future missions to explore similar objects. The findings, published in The Astrophysical Journal, represent a milestone in the quest to understand the origins of the most energetic particles in the universe.