Microscopic ‘timers’ reveal likely source of cosmic rays: NASA

Microscopic “timers” have revealed the likely source of galactic radiation that we detect at Earth. Most of the cosmic rays originated relatively recently in the nearby clusters of massive stars, according to new results from NASA’s Advanced Composition Explorer (ACE) spacecraft.

ACE allowed the research team to determine the source of these cosmic rays by making the first observations of a very rare type of cosmic ray that acts like a tiny timer, limiting the distance the source can be from Earth.

“Before the ACE observations, we didn’t know if this radiation was created a long time ago and far, far away, or relatively recently and nearby,” said co-author Eric Christian.

The galactic cosmic rays detected by ACE that allowed the team to estimate the age of the cosmic rays, and the distance to their source, contain a radioactive form of iron called Iron-60 (60Fe). It is created inside massive stars when they explode and then blasted into space by the shock waves from the supernova.

Some 60Fe in the debris from the destroyed star is accelerated to cosmic-ray speed when another nearby massive star in the cluster explodes and its shock wave collides with the remnants of the earlier stellar explosion.

“Our detection of radioactive cosmic-ray iron nuclei is a smoking gun indicating that there has likely been more than one supernova in the last few million years in our neighborhood of the Galaxy,” said lead author Robert Binns of Washington University.

This research is published in Science.