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Age-old mystery of cosmic rays finally solved


The source of cosmic rays is supernovae, or exploding stars, researchers have proved. IMAGE CREDIT: Greg Stewart, SLAC National Accelerator Laboratory


The cosmic rays bombarding the Earth come from exploding stars, scientists have finally proved.

For every minute you sit here reading this, your head is being penetrated by approximately two hundred secondary particles created by these of cosmic rays -- each with an energy of more than a billion electron volts.

Yet despite their ubiquity, astrophysicists could never prove cosmic rays' source.

"This is really one of the big unsolved puzzles in astrophysics," said Stefan Funk, lead author of the study, which appears in the journal Science this week. Funk, a physics professor at Stanford University, spoke to reporters at the AAAS Annual Meeting in Boston.

Now, Funk and his research team have linked distinctive gamma ray signatures from exploding stars -- supernovas -- to the cosmic rays hitting Earth.

By combing through data from Fermi's Large Area Telescope, the team was able to provide a "smoking gun" direct connection between cosmic rays and two supernovae, the forgettably named W44 and IC 443. Both are around 10,000 years old.

Cosmic rays were discovered in 1912 by Victor Hess, who realized during balloon flights that radiation increased at higher altitudes. Hess won Nobel Prize for that discovery.

Soon after, scientists began surmising that cosmic rays come from exploding stars. Cosmic rays are incredibly energetic -- their acceleration is much, much greater than can be achieved even in massive particle accelerators like the Large Hadron Collider -- so astrophysicists assumed they must originate from an incredibly energetic source.

But scientists lacked proof that supernovas were the ultimate source.

Cosmic rays (which are not actually rays) are created when particles pass back and forth between the shock wave that pushes outwards as stars explode.

Kate Allen is the Star's global science and technology reporter. She is reporting from the AAAS meeting in Boston this week. Follow her on Twitter @katecallen


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Alas, I still haven't received any of the powers of The Fantastic Four.

What is exploding here is not a star, but a plasma double layer. Exploding double layers are the (largely unacknowledged) source of most of the gamma ray emissions in space. And they have NOTHING to do with shock waves. The latter are a silly fiction.

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