💥 A universal feature discovered in all cosmic rays

The international cosmic ray observation mission reveals a key feature of these rays, marking a major advance in understanding their origin.

A century after their discovery, cosmic rays - those extremely energetic particles from the far reaches of the universe - remain a mystery to scientists. The DAMPE space telescope (Dark Matter Particle Explorer) is tackling this phenomenon, particularly exploring the role that dark matter might play in their formation.


This international mission, which includes the University of Geneva (UNIGE), now makes a major breakthrough by highlighting a universal feature of these rays. The results are published in the journal Nature.

Cosmic rays are the most energetic particles observed in the universe, far surpassing the energy of particles produced by artificial accelerators on Earth. Their exact origin is still being studied, and they are thought to come from extreme astrophysical phenomena, such as supernovae, black hole jets or pulsars.

The DAMPE space telescope, launched in December 2015, is expected to provide answers about the origin and nature of cosmic rays. This space mission, to which the astroparticle physics group of the Department of Nuclear and Particle Physics (DPNC) at UNIGE is one of the main contributors, today reports a crucial breakthrough.

Thanks to the analysis of high-precision measurements collected by the telescope, scientists have succeeded in highlighting a universal feature in the energy spectra of primary cosmic ray nuclei, from protons to iron.

"Cosmic rays are mainly composed of protons but also of helium, carbon, oxygen and iron nuclei," explains Andrii Tykhonov, associate professor at the Department of Nuclear and Particle Physics of the Section of Physics at the Faculty of Science of UNIGE, co-author of the study.

"These rays are also distributed 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."

These results constitute an important step towards a more complete understanding of the origin of cosmic rays and the mechanisms that govern their propagation.

A new common feature

The results show that, for all studied nuclei, the number of particles decreases more and more rapidly beyond a certain value. This phenomenon is called "spectral softening". Normally, the number of particles already decreases as energy increases, but here this decrease becomes even more pronounced. It occurs around a rigidity of about 15 TV (teravolts).

A particle's rigidity measures the resistance of its trajectory in a magnetic field. The observation of a common structure at this rigidity strongly supports models that explain that cosmic ray acceleration and transport depend on particle rigidity.

In contrast, alternative models, which suggest that energy per nucleon (energy divided by the number of nucleons in the particle) would be a key factor, are strongly invalidated by these measurements, with a certainty of 99.999%.

The Geneva team played a central role in this scientific breakthrough. In particular, they developed advanced artificial intelligence techniques for reconstructing detected events and contributed to key measurements of proton and helium fluxes, as well as carbon analysis.

The group also led the development of one of DAMPE's major sub-detectors, the Silicon-Tungsten Tracker (STK), an essential instrument for precise reconstruction of particle trajectories and measurement of their charge.

These results constitute an important step towards a more complete understanding of the origin of cosmic rays and the mechanisms governing their propagation in the Galaxy. They provide new experimental constraints on acceleration models in astrophysical sources and on particle transport in the interstellar medium, thus paving the way for a more accurate description of high-energy particle populations.