New Measurements of Cosmic Ray Spectra Favour Charge Over Mass

Astrophysicists have confirmed that the 'brakes' applied to high-energy particles are determined by electric charge, a measurement previously hindered by the extreme difficulty of isolating individual heavy nuclei at teravolt scales. The Dark Matter Particle Explorer (DAMPE) has directly measured the **cosmic ray spectra** of carbon, oxygen, and iron, identifying a distinct softening at approximately 15 teravolts. This rigidity-dependent break suggests that the source or propagation of these particles relies on electric charge rather than atomic mass.

Deciphering Cosmic Ray Spectra

For decades, researchers debated whether spectral features depended on a particle’s mass or its charge. Earlier experiments often relied on indirect ground-based observations that struggled to separate chemical species at high energies, whereas DAMPE’s orbital vantage point allows for direct identification of elements as they traverse the galaxy. DAMPE analysed nine years of orbital data, tracking nuclei from 20 gigavolts up to 100 teravolts. The researchers observed that the spectral index—the slope of the energy distribution—changes sharply at the 15-teravolt mark for all measured species. Statistical analysis rejects mass-dependent softening at a confidence level exceeding 99.999%. While the 15-teravolt feature is now statistically certain, its origin remains a subject of theoretical debate. The data suggests a common origin or a shared physical barrier in the interstellar medium. Potential explanations include:

• A single, relatively nearby cosmic ray accelerator.
• Specific diffusion effects in local magnetic fields.
• A limit in the acceleration capacity of supernova remnants.

This finding aligns heavy nuclei with previously observed proton and helium data. However, the study does not identify the specific astronomical object responsible for this universal 15-teravolt feature.