Cosmic rays, high-energy particles, can damage electronics on Earth, as well as human and non-human DNA, which puts astronauts in space at risk but has also caused any number of genetic modifications in plants that are considered completely natural.  

Their origin has confounded scientists for decades. A study using data  collected by IceTop at the IceCube Neutrino Observatory at the South Pole, reveals new information that may help unravel the longstanding mystery of exactly how and where these "rays", because the more scientists learn about the energy spectrum and chemical composition of cosmic rays, the closer humanity will come to uncovering where these energetic particles originate. 

Cosmic rays are known to reach energies above 100 billion giga-electron volts (1011 GeV). The data reported in this latest paper cover the energy range from 1.6 times 106 GeV to 109 GeV. Researchers are particularly interested in identifying cosmic rays in this interval because the transition from cosmic rays produced in the Milky Way Galaxy to "extragalactic" cosmic rays, produced outside our galaxy, is expected to occur in this energy range. 


The cosmic ray energy spectrum, shows the steepening at the "knee." Below the knee, cosmic rays are galactic in origin; above that energy, particles from more distant regions in our universe become more and more likely. Credit: Bakhtiyar Ruzybayev/University of Delaware

Exploding stars called supernovae are among the sources of cosmic rays here in the Milky Way, while distant objects such as collapsing massive stars and active galactic nuclei far from the Milky Way are believed to produce the highest energy particles in nature.

As University of Delaware physicist Bakhtiyar Ruzybayev, the study's corresponding author, points out in the scientific figure (above) submitted to the journal, the cosmic-ray energy spectrum does not follow a simple power law between the "knee" around 4 PeV (peta-electron volts) and the "ankle" around 4 EeV (exa-electron volts), as previously thought, but exhibits features like hardening around 20 PeV and steepening around 130 PeV.

"The spectrum steepens at the 'knee,' which is generally interpreted as the beginning of the end of the galactic population. Below the knee, cosmic rays are galactic in origin, while above that energy, particles from more distant regions in our universe become more and more likely," Ruzybayev explained. "These measurements provide new constraints that must be satisfied by any models that try to explain the acceleration and propagation of cosmic rays."

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