The origin of cosmic rays in the universe
has confounded scientists for decades. But a study by researchers using
data from 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" (they are
actually high-energy particles) are produced.
Cosmic rays can damage electronics on Earth, as well as human DNA, putting astronauts in space especially at risk.
The research, which draws on data collected by IceTop, the IceCube Observatory's surface array of detectors, is published online in Physical Review D, a leading journal in elementary particle physics.
University of Delaware physicist 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 coordination by
the project office at the University of Wisconsin, Madison.
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.
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 Ruzybayev points out in a scientific figure 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."
Ice
Top consists of 81 stations in its final configuration, covering
an area of one square kilometer on the South Pole surface above the
detectors of IceCube, which are buried over a mile deep in the ice. The
analysis presented in this article was performed using data taken from
June 2010 to May 2011, when the array consisted of only 73 stations.
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