NANJING -- A Chinese research team has found that high-energy cosmic rays may travel more slowly than expected after analyzing data from the country's Dark Matter Particle Explorer Satellite "Wukong."

Galactic cosmic rays are energetic particles travelling through the universe nearly at the speed of light. They are messengers of the violent evolution of stars or stellar systems in extreme environments. Some scientists have proposed that dark matter could form part of cosmic rays.

There are generally two classes of cosmic rays. Carbon and oxygen nuclei are the primary ones and are believed to be accelerated at astrophysical sources like a supernova explosion. Boron nuclei belong to the secondary class and are thought to be mainly produced by the fragmentation of heavier nuclei, such as carbon and oxygen, via collisions with interstellar matter during their space travel.

From 2016 to 2021, DAMPE collected more than 3.5 million carbon, oxygen and boron nuclei. This enabled Chinese scientists to measure the cosmic ray boron-to-carbon and boron-to-oxygen flux ratios with an unprecedented precision in an energy range from 0.01 TeV/n to 5.6 TeV/n and they found that their energy spectra significantly differed from that predicted by conventional turbulence theories of the interstellar medium.

Chang Jin, DAMPE chief scientist and academician of the Chinese Academy of Sciences, told Xinhua in an interview that it is the first time this satellite had managed to precisely measure the ratio of primary and secondary particles in cosmic rays.

It detected an unexpected new energy spectral structure, which suggests that the classical cosmic rays propagation model may need to be modified, said Chang.

The spectral hardening in cosmic ray boron-to-carbon and boron-to-oxygen flux ratios is probably because the high-energy particles travel more slowly in the universe than expected, explained Yue Chuan, an associate researcher of the DAMPE team from the Purple Mountain Observatory (PMO).

Yuan Qiang, a researcher of the DAMPE team from the PMO, said that when primary particles travel more slowly, they have more chances to collide with the interstellar medium, which will produce more secondary particles.

The findings have been published in the journal Science Bulletin.

"Wukong" was launched on Dec. 17, 2015, to observe cosmic rays and gamma rays and search for evidence of the existence of dark matter particles.

The team revealed that they are also working on the Very Large Area Gamma-ray Space Telescope (VLAST). It will result in a 50-fold improvement in the ability to detect gamma-rays, which will also help to better detect signals of dark matter in gamma-ray emissions in the future.