An international cohort of astrophysicists from Italy, Japan, and the United States has gathered evidence pointing to the universe’s most energetic radiation sources within our own Milky Way. The emitted energies exceed what any terrestrial particle accelerator can achieve by tens of millions of times, and the findings appear in a leading physics journal, Physical Review Letters (PRL) (CALET team, updated synthesis).
Ultra-high-energy cosmic rays have intrigued scientists since their discovery in 1962. While their origins remain partly mysterious, researchers have long noted similar radiation surges from celestial objects beyond the Milky Way. The latest results, however, suggest that some of the most intense cosmic rays could originate much closer to home than previously thought (CALET collaboration, contemporaneous analysis).
Recent measurements with the CALET Calometric Electron Telescope aboard the International Space Station indicate at least three potential galactic sources of ultra-high-energy cosmic rays, all situated roughly 3,000 light-years from Earth. This localisation within our galaxy marks a significant step in mapping how extreme particle energies arise in familiar stellar environments (CALET data interpretation).
CALET recorded its first high-energy event in October 2015, and since then has catalogued seven million cosmic-ray events. The instrument has detected energies extending beyond 10 teravolts, a substantial advancement over earlier studies that identified cosmic rays up to around 4 teravolts. These thresholds help refine models of particle acceleration in galactic remnants and the interstellar medium (CALET findings excerpts).
The leading candidate for the origin of these ultra-high-energy rays is a supernova remnant within the Vela constellation, about 800 light-years away. The progenitor star exploded roughly 11,000 years ago, creating a powerful accelerator environment capable of propelling particles to extreme energies (regional astrophysical analysis).
Researchers plan to extend CALET’s measurements of galactic cosmic-ray sources through the remaining years of the International Space Station’s operational life. With ISS retirement anticipated toward the end of this decade, ongoing observations will be crucial for confirming source identities and understanding the long-term evolution of energetic particle acceleration in our galaxy (ongoing program notes).
Beyond the immediate scientific implications, astrophysicists remain mindful of the broader context. Earlier warnings from past decades emphasized the potential threats to life on Earth from close encounters with neutron stars and other compact objects, underscoring the importance of monitoring the dynamic high-energy universe from a safe, distant vantage point (historical cautions in high-energy astronomy).