Cosmic rays are last gasp of dying stars: scientists

Scientists have cracked a long-standing mystery surrounding the source of cosmic rays, a form of high-energy radiation emanating from deep space that continually crashes into the earth's atmosphere.

The rays, mostly made up of high-energy protons, stream through the galaxy and interact with air molecules high in the earth's upper atmosphere, creating showers of charged particles, some of which reach the ground.

Though ubiquitous, the origin of cosmic rays has never been pinned down. Scientists have suggested that they could either come from the remains of supernovae, which are the violent explosions that mark the death of the biggest stars, or they could be particles accelerated by black holes somewhere outside our galaxy.

"The energies of these protons are far beyond what the most powerful particle colliders on earth can produce," said Professor Stefan Funk, an astrophysicist with the Kavli Institute and Stanford University, who led the latest work. "In the last century, we've learned a lot about cosmic rays as they arrive here. We've even had strong suspicions about the source of their acceleration, but we haven't had unambiguous evidence to back them up until recently."

People on the ground are shielded from any harmful effects of cosmic rays thanks to the earth's thick atmosphere. The higher up you go - flying in a plane, for example - the higher the dose of radiation you receive.

The greatest hazards from cosmic rays, however, are faced by astronauts floating above the earth - and possibly one day travelling to Mars. The doses of radiation individuals would experience on a long-duration space flight are one of the major limiting factors to human missions beyond earth.