Magazine article Science News

Origin of Cosmic Rays Questioned: PAMELA Data Suggest That Supernovas Aren't Only Source

Magazine article Science News

Origin of Cosmic Rays Questioned: PAMELA Data Suggest That Supernovas Aren't Only Source

Article excerpt

The confirmed origin of ordinary cosmic rays may need to be unconfirmed. New data gathered by an instrument aboard a Russian spacecraft challenge the theory that most cosmic rays are fueled by supernovas, the explosions created by dying stars.

"The mechanism for the acceleration of cosmic rays needs to be completely revised," says Piergiorgio Picozza, a physicist at the University of Rome Tor Vergata in Italy. Picozza is a coauthor of a paper posted online March 3 in Science detailing new observations from PAMELA, the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics.

Cosmic rays aren't actually rays. They're fast-moving particles that carry an extraordinary amount of energy and continuously bombard the Earth from every direction. The most popular explanation for the origin of these particles points to shock waves created by far-off supernovas, one of the few phenomena powerful enough to impart such energy.

According to that explanation, clouds of charged gas rush outward during a supernova and generate strong magnetic fields. These magnetic fields could accelerate charged particles to tremendous speeds and eject them into space.

Orbiting hundreds of kilometers above Earth, PAMELA spent three years collecting cosmic ray particles--mostly hydrogen and helium nuclei with energies ranging from a billion to a trillion electron volts, comparable to the energy of particles collided in the biggest particle accelerator in the United States.

A supernova should accelerate both hydrogen and helium in the same way. …

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