The origin of cosmic rays in the universe has confounded scientists for decades. But a study by researchers using data from the IceCube Neutrino Observatory¹ at the South Pole reveals new information that may help unravel² the longstanding mystery of exactly how and where these "rays" (they are actually high-energy particles) are produced. Cosmic rays can damage electronics on Earth, as well as human DNA³, putting astronauts in space especially at risk.

 

The research, which draws on data collected by IceTop, the IceCube Observatory's surface array of detectors⁴, is published online in Physical Review D, a leading journal in elementary particle physics.

 

University of Delaware physicist⁵ Bakhtiyar Ruzybayev is the study's corresponding author. UD scientists were the lead group for the construction of IceTop with support from the National Science Foundation and coordination⁶ by the project office at the University of Wisconsin, Madison.

 

The more scientists learn about the energy spectrum⁷ 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 volts⁸ (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 interval⁹ because the transition from cosmic rays produced in the Milky¹⁰ Way Galaxy¹¹ to "extragalactic" cosmic rays, produced outside our galaxy, is expected to occur in this energy range.

 

Exploding stars called supernovae are among the sources of cosmic rays here in the Milky Way, while distant objects such as collapsing¹² massive stars and active galactic nuclei¹³ far from the Milky Way are believed to produce the highest energy particles in nature.

 

As Ruzybayev points out, 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 previously¹⁴ 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 constraints¹⁵ that must be satisfied by any models that try to explain the acceleration¹⁶ and propagation（传播，繁殖） of cosmic rays."

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