Milky Way proton PeVatron identified by international research team

An international team of researchers has identified a source of extremely high-energy protons within the Milky Way, marking a significant step in understanding the origins of cosmic rays. The discovery, published in The Astrophysical Journal on July 16, 2026, confirms that a region known as LHAASO J1912+1014u acts as a proton PeVatron — a cosmic accelerator capable of producing particles with energies exceeding one quadrillion (1015) electron volts, or a petaelectron volt (PeV).

The findings were led by Tsunefumi Mizuno, an associate professor at Hiroshima University’s Hiroshima Astrophysical Science Center, who described the discovery as a culmination of multiwavelength observations from three major observatories: NASA’s Fermi Gamma-ray Space Telescope, the Nobeyama 45-meter telescope’s FOREST Unbiased Galactic Plane Imaging Survey (FUGIN), and the Chandra X-ray Observatory. These instruments provided data across a broad range of electromagnetic wavelengths, enabling the team to rule out alternative explanations and confirm the source’s role as a PeVatron.

LHAASO J1912+1014u, located in the constellation Aquila near the star Altair, was initially classified as a supernova remnant. However, emissions above 100 TeV detected by the Large High Altitude Air Shower Observatory (LHAASO) in 2024 prompted further investigation. The team’s analysis revealed that the gamma-ray emission from the region extends smoothly from over 100 trillion electron volts (TeV) down to 400 million electron volts (MeV), a pattern inconsistent with electron-based acceleration mechanisms. Additionally, the distribution of gamma rays aligned with interstellar gas traced by FUGIN radio data, while Chandra X-ray observations showed minimal diffuse emission, both supporting the proton PeVatron hypothesis.

“This research is achieved by team effort. There is an old Japanese saying: ‘One arrow is easy to break, but three arrows bundled together are not,’” Mizuno said. “In this study, three arrows — Fermi-LAT GeV gamma-ray data, FUGIN radio data, and Chandra X-ray data, are bundled together through a detailed multiwavelength modeling, revealing that our target, LHAASO J1912+1014u, is a cosmic-ray proton PeVatron.”

The study’s results highlight the role of multiwavelength observations in resolving cosmic ray sources. Cosmic rays, primarily composed of protons with trace electrons, are among the most energetic particles in the universe, surpassing the capabilities of human-made accelerators like the Large Hadron Collider. The identification of LHAASO J1912+1014u as a PeVatron provides critical insights into the mechanisms that accelerate particles to such extreme energies, with implications for understanding galactic-scale astrophysical processes.

Mizuno emphasized that the discovery not only identifies a specific PeVatron but also characterizes the properties of accelerated particles. With dozens of potential PeVatron candidates in the Milky Way, the team plans to investigate other regions to refine models of cosmic ray acceleration. The findings could also inform future neutrino and cosmic ray observatories, which rely on precise predictions of particle distribution to detect rare interactions.

The research underscores the collaborative nature of modern astrophysics, with contributions from institutions across Japan, the United States, and Europe. As scientists continue to map the Milky Way’s high-energy landscape, the identification of LHAASO J1912+1014u represents a pivotal milestone in unraveling the mechanisms that shape the universe’s most extreme environments.