SAN DIEGO - For decades, astronomers have sought to pin down a source for ultra high-energy cosmic rays. The distant sources must be among the more powerful events in the universe, perhaps the creation of black holes or the mergers of galaxies.
It appears the first source has been located, a finding that would be considered a major breakthrough in the field.
If proved out, it represents the first time scientists are able to study a known object from beyond our galaxy by examining actual material (stuff like what you and everything else is made of) instead of electromagnetic radiation (radio waves, visible light, X-rays and so on).
Cosmic rays are not actually rays, like light. They are instead subatomic particles, thought to be mostly protons, on of the fundamental units of matter. The highest-energy versions of them race across the universe at more than 99.9 percent of light-speed, packing in their tiny bodies more punch than a golf ball hit by a pro, explained physicist Glennys Farrar of New York University.
The particles are difficult to study, because most break up in Earth's atmosphere. Only a handful ever reach the planet.
When cosmic rays break apart, however, they create billions of lower-energy particles. Arrays of detectors on the ground record these secondary particle showers -- some here, some a mile or so over there -- and scientists then calculate the direction from which the original cosmic ray must have come.
They come from everywhere, scientists learned years ago.
Muddling it all further, the ultra high-energy particles get jostled around by magnetic fields during their travels across space, so upon detection they can appear to have started at a slightly different location than they really did.
If it all sounds like smoke and mirrors, then you've grasped the frustration scientists feel. Nobody has ever firmly tied a thing in the sky an ultra high-energy cosmic ray. (A separate recent study identified a source of lower-energy cosmic rays here in our own galaxy.)
In the new research, Farrar and her colleagues identified five cosmic rays over a 10-year period that all come from one small circle in the sky. It is likely, she said, that they were all spawned from the same source. Like motorists taking different paths through a city, however, they each arrived at their own pace and took a slightly different parking slot.
Other observations of that same circle of sky reveal a colossal merger of two clusters of galaxies, about 450 million light-years away. A light-year is the distance light travels in a year, about 6 trillion miles (10 trillion kilometers).
Farrar can't be certain the merger is the source of the cosmic rays, but that's her bet for now. The merger would fuel huge magnetic shock waves that could accelerate particles with tremendous force. The galaxies in the cluster could also be home to quasars or gamma-ray bursts that might have produced the fast-flying particles.
"Stuff we're made out of has come from well outside our galaxy, travelling millions of light-years," Farrar said in an interview.
The results were presented here last week at a meeting of the American Astronomical Society and will be detailed in the Astrophysical Journal. The observations were made with Japan's Akeno Giant Air Shower Array and the National Science Foundation's High Resolution Fly's Eye Air Flourescence Detector.
Other cosmic ray detections that have been made but not yet released could confirm the finding.
This article is part of SPACE.com's weekly Mystery Monday series.
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