Radio receivers record cosmic rays hitting Earth

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A small prototype array in Germany has detected several radio flashes from cosmic rays that smack into the Earth's upper atmosphere. A larger array, with more of these low-cost radio antennas, could help astrophysicists decipher the mystery behind the highest energy cosmic rays.

Cosmic rays are high-speed sub-atomic particles - mostly nuclei and protons - that zip around space in all directions. Lucky for us, they cannot plow very far into our atmosphere before they collide with a gas molecule.

From these collisions come showers of secondary particles - including electrons, anti-electrons (called positrons), and muons, which are like heavy electrons. Cosmic rays can be characterized by the showers they produce.

Surprisingly, some of these space-faring projectiles have a 100 million times more energy than is possible in man-made accelerators. There are no "cosmic accelerators" in our galactic neighborhood that seem powerful enough to generate particles with this much energy.

Therefore, these so-called ultra-high energy cosmic rays (UHECRs) presumably come from colliding galaxies or large black holes hundreds of millions of light years away. But that raises a problem: cosmic "stuff" along the way will slow - or even outright destroy - high-energy particles traveling these great distances.

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