After 100 years, scientists finally uncover hidden rule behind cosmic rays

Cosmic rays are the highest energy particles ever observed in nature. They carry far more energy than particles produced by even the most advanced accelerators on Earth. Scientists believe they are created by some of the universe's most violent events, including supernova explosions, jets from black holes, and pulsars.

Launched in December 2015, the DAMPE space telescope was designed to investigate the nature of cosmic rays and explore possible connections to dark matter. The mission includes major contributions from the astrophysics group at the Department of Nuclear and Particle Physics (DPNC) at the University of Geneva (UNIGE).

By examining highly precise data collected by DAMPE, researchers discovered a universal pattern in the energy spectra of primary cosmic ray nuclei, ranging from lightweight protons to much heavier iron nuclei.

"Cosmic rays are primarily composed of protons, but also of helium, carbon, oxygen, and iron nuclei,'' explains Andrii Tykhonov, associate professor at the DPNC in the Faculty of Science at UNIGE, and co-author of the study. "These particles are also categorised according to their energy: low, up to a few billion electron-volts; intermediate, from a few billion to several hundred billion electron-volts; and high, from 1,000 billion electron-volts and beyond."

Scientists Discover a Shared Cosmic Ray Pattern

The research showed that for every type of nucleus studied, the number of particles begins dropping much faster after reaching a certain threshold. Scientists refer to this effect as "spectral softening."

Normally, higher-energy cosmic rays become less common as energy increases. However, the DAMPE observations revealed that the decline becomes dramatically steeper beyond a rigidity of roughly 15 TV (teraelectron-volts). Rigidity describes how strongly a particle's path resists being bent by magnetic fields.

Because this same feature appears across many different types of particles, the findings strongly support theories suggesting that cosmic ray acceleration and movement through space are controlled by rigidity. At the same time, the data largely rules out competing explanations based on energy per nucleon (energy divided by the number of nucleons in the particle). According to the researchers, the confidence level against those alternative models reaches 99.999%.

AI and Advanced Detectors Help Drive the Discovery

Researchers from Geneva played a major role in the breakthrough. The team developed sophisticated artificial intelligence methods to reconstruct particle events detected by the telescope. They also contributed to important measurements involving proton and helium fluxes and helped analyze carbon nuclei data.

In addition, the Geneva group led the development of one of DAMPE's key instruments, the Silicon-Tungsten Tracker (STK). This detector is essential for accurately tracing particle paths and determining the electrical charge of incoming cosmic rays.

The findings mark an important advance in understanding how cosmic rays are created and how they travel through the galaxy. Scientists say the new results place tighter limits on existing models of particle acceleration in astrophysical sources and improve our understanding of how high-energy particles move through interstellar space.