Cosmic Rays: They Aren't What We Thought They Were

By Nancy Atkinson - April 19, 2012 01:38 PM UTC | Physics

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The origin of cosmic rays has been one of the most enduring mysteries in physics, and it looks like it's going to stay that way for a while longer. One of the leading candidates for where cosmic rays come from is gamma ray bursts, and physicists were hoping a huge Antarctic detector called the IceCube Neutrino Observatory would confirm that theory. But observations of over 300 GRB's turned up no evidence of cosmic rays. In short, cosmic rays aren't what we thought they were.

But, just like Thomas Edison who said that "every wrong attempt discarded is another step forward," physicists view this latest finding as progress.

"Although we have not discovered where cosmic rays come from, we have taken a major step towards ruling out one of the leading predictions," said IceCube principal investigator and University of Wisconsin–Madison physics professor Francis Halzen.

Cosmic rays are electrically charged particles, such as protons, that strike Earth from all directions, with energies up to one hundred million times higher than those created in man-made accelerators. The intense conditions needed to generate such energetic particles have focused physicists' interest on two potential sources: the massive black holes at the centers of active galaxies and gamma ray bursts (GRBs), flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies.

IceCube is using neutrinos, which are believed to accompany cosmic ray production, to explore these two theories. In a

paper published in the April 19 issue of the journal Nature,

IceCube scientists describe a search for neutrinos emitted from 300 gamma ray bursts observed, most recently in coincidence with the SWIFT and Fermi satellites, between May 2008 and April 2010. Surprisingly, they found none - a result that contradicts 15 years of predictions and challenges one of the two leading theories for the origin of the highest energy cosmic rays.

[caption id="attachment_94704" align="aligncenter" width="580" caption="Aurora seen behind the IceCube Lab. Photo by: Sven Lidstrom/NSF"]

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The detector searches for high-energy (teraelectronvolt; 10

12

-electronvolt) neutrinos, and in their paper the team said they found an upper limit on the flux of energetic neutrinos associated with GRBs that is at least a factor of 3.7 below the predictions. This implies that either GRBs are not the only sources of cosmic rays with energies greater than 10

18

More info on IceCube.

Paper in Nature.

Source:

IceCube/University of Wisconsin

Nancy Atkinson

Nancy Atkinson

Nancy Atkinson is a space journalist and author with a passion for telling the stories of people involved in space exploration and astronomy. She is currently retired from daily writing, but worked at Universe Today for 20 years as a writer and editor. She also contributed articles to The Planetary Society, Ad Astra (National Space Society), New Scientist and many other online outlets.

Her 2019 book, "Eight Years to the Moon: The History of the Apollo Missions,” shares the untold stories of engineers and scientists who worked behind the scenes to make the Apollo program so successful, despite the daunting odds against it. Her first book “Incredible Stories From Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos” (2016) tells the stories of 37 scientists and engineers that work on several current NASA robotic missions to explore the solar system and beyond.

Nancy is also a NASA/JPL Solar System Ambassador, and through this program, she has the opportunity to share her passion of space and astronomy with children and adults through presentations and programs. Nancy's personal website is nancyatkinson.com