Something strange may be going on around Orion. Somewhere near that familiar constellation, two unknown sources seem to be showering Earth and the rest of the Milky Way with galactic cosmic rays, astronomers report today. The findings could shed light on one of the biggest mysteries in the universe.
The term "cosmic rays" is somewhat of a misnomer. The "rays" consist mostly of solid protons, not the photons that make up light. These particles whiz around the cosmos at near-light speed, causing all sorts of mischief when they penetrate Earth's magnetic field. Scientists blame them for everything from computer-memory glitches to bolts of lightning. In space, the rays would pose a health hazard to astronauts on interplanetary missions, as they can mutate our DNA (ScienceNOW, 4 November).
Despite decades of study, researchers still don't know the basics about cosmic rays, including what causes them and where they come from. Supposed sources include supernovae, quasars, and black hole collisions (ScienceNOW, 4 October 2007). But until now, no one has connected cosmic-ray generation to a single event. And no one has been able to pinpoint a source; cosmic rays seem to emanate more or less consistently from all over the sky.
Or perhaps not, a team from 16 institutions reports in Physical Review Letters. Using the Milagro observatory in Los Alamos, New Mexico, which detects cosmic-ray particles when they collide with water molecules in a pool on the ground, the researchers compiled nearly 7 years' worth of data on about 220 billion cosmic-ray collisions. Based on those data, the researchers have found that two swaths of sky over the Northern Hemisphere--about where Orion sits--seem to be producing more cosmic rays than any other. The difference isn't much--about 0.06% and 0.04%, respectively--but it's enough to stick out from the background activity. So far, the researchers say, they have ruled out the possibility of the zones being somehow caused by our sun or by the direction of the rays being warped by Earth's magnetic field. Other than that, however, the book is still open about what's causing these rays in the first place.
Astrophysicist John Wefel of Louisiana State University in Baton Rouge, who authored a paper in last week's issue of Nature describing a similar discovery involving high-energy-electron cosmic rays, says both findings should stimulate a determined search for candidate sources. "It's not like [the hot spots] are standing way out from the background," he says, "but the fact that they're there at all is really interesting."