Cosmic Rays – A Mystery Solved?

When I was a kid, the reigning answer to the question “Where do cosmic rays come from?” was “Um… Dunno. Sorry, kid.”

But hey! The day I went first went to college, I thought “Finally. I’ll be able to find more than two pages on Pluto, including pictures of the star field it’s in.” Of course, Abell had (wait for it) two pages on Pluto, including the star field pictures…

The most likely explanation for the origin of cosmic rays is indeed, that all purpose answer to every astronomical mystery, black holes.

Scientists of the Pierre Auger Collaboration announced today (8 Nov. 2007) that active galactic nuclei are the most likely candidate for the source of the highest-energy cosmic rays that hit Earth. Using the Pierre Auger Observatory in Argentina, the largest cosmic-ray observatory in the world, a team of scientists from 17 countries found that the sources of the highest-energy particles are not distributed uniformly across the sky. Instead, the Auger results link the origins of these mysterious particles to the locations of nearby galaxies that have active nuclei in their centers. The results appear in the Nov. 9 issue of the journal Science.

Active Galactic Nuclei (AGN) are thought to be powered by supermassive black holes that are devouring large amounts of matter. They have long been considered sites where high-energy particle production might take place.

Why has this problem been so hard? To understand, know that cosmic rays are probably misnamed. The term was coined in the ’40s and popularized in the ’50s, when “death rays” and X-rays and laser-rays were very cool ways to attack alien monsters intent on stealing our women, or something. Cosmic rays are actually charged particles, and fairly heavy ones at that, that have been accelerated to amazingly high speeds, sometimes near the speed of light. Some of the energies involved were difficult to explain, to say the least. And the fact that these energetic particles were charged, meant that their paths were subject to the whims and fancies of magnetic fields throughout the galaxy. The sources of the cosmic rays was deemed impossible to determine. But that was then.

This study showed the correlation of active galaxies, and hence, their super-massive black-hole cores, with cosmic rays.

It is also in contradiction with studies that show magnetic fields near supernova have the potential to accelerate charged particles the same way.

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