A global team of astrophysicists spanning Europe, Asia, and North America has assembled compelling evidence about some of the universe’s most energetic radiation sources nestled within our own Milky Way. The energies observed dwarf what human-made particle accelerators can achieve, marking a landmark in understanding how cosmic particles reach extraordinary power in familiar galactic settings.
Ultra-high-energy cosmic rays have intrigued researchers since their discovery in the early 1960s. While the exact birthplace of these extreme particles remains partly enigmatic, scientists have long noted bursts of similar radiation from celestial objects beyond our galaxy. The latest results, however, point to the possibility that a portion of the loftiest cosmic rays originate much closer than previously imagined, residing in our galactic neighborhood rather than in distant realms.
Measurements from the CALET Calorimetric Electron Telescope aboard the International Space Station indicate at least three credible galactic sources of ultra-high-energy cosmic rays, each located roughly 3,000 light-years from Earth. Locating these origins within the Milky Way represents a meaningful step toward mapping how particles are accelerated to extraordinary energies in well-known stellar environments.
Since its first high-energy event in October 2015, CALET has recorded millions of cosmic-ray events. The instrument has detected energies extending well beyond the 10-teravolt range, marking a substantial advance from earlier studies that identified cosmic rays up to about 4 teravolts. These observations refine models of how particle acceleration unfolds in remnants of stellar explosions and within the interstellar medium.
The leading candidate for the source 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 dynamic environment that acts as a natural accelerator capable of propelling particles to extreme energies in the surrounding space.
Researchers intend to continue CALET’s measurements of galactic cosmic-ray sources throughout the remaining years of the International Space Station’s operation. With the ISS retirement anticipated toward the end of this decade, ongoing observations will be essential for confirming source identities and for understanding how energetic particle acceleration evolves over time in our galaxy.
Beyond the immediate scientific implications, scientists maintain a broader perspective. Earlier cautions from past decades highlighted the potential risks to life on Earth from close encounters with neutron stars and other compact objects, underscoring the importance of monitoring the high-energy universe from a safe, distant vantage point.