High-Energy Cosmic Rays

PureInsight | January 2, 2001

Earth's atmosphere is regularly bombarded by very small numbers of incredibly energetic cosmic ray particles, a type discovered less than a decade ago. No one can explain where they come from or why.

Less energetic cosmic ray particles have long been known to bathe our planet. Hundreds slam into every square yard (or square meter) of Earth's atmosphere every second. Many are thought to originate within our galaxy, spawned by large exploding stars called supernovae.

Earth's atmosphere destroys the particles, protecting us. (Astronauts on space walks, on the other hand, are exposed to the potentially deadly particles and must limit time spend outside their craft.)

A decade ago, a new type of cosmic ray particle was discovered, one far more energetic (and much more rare) than the more common type previously known.

'How these microscopic particles achieve macroscopic energies is one of the most pressing questions of high-energy astrophysics,' says Niel Brandt, assistant professor of astronomy and astrophysics at Penn State. 'These particles cannot travel far through the universe because interactions with the cosmic microwave background quickly sap their energy, so they must be created relatively nearby.'

But no one can find the source.

Brandt and others speculate that the particles might come from some unknown super powerful cosmic explosion, from a huge black hole, or could possibly represent exotic remnants of the early universe.

(Image: Dust swirls into the center of a galaxy, presumably to a black hole. The process may create high-energy cosmic rays. )


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