High-energy cosmic rays have extragalactic origin

More high-energy cosmic rays are coming from a specific direction that lies outside the Milky Way galaxy, leading astronomers to conclude they have an extragalactic origin.

Ian Marsh | Sep 27, 2017

An international team of 400 researchers from 18 nations has concluded that high-energy cosmic rays originate from outside the Milky Way galaxy.

The study is published in the journal Science.

The researchers looked at more than ten years of data collected by the Pierre Auger Observatory in the Argentinian Pampas and discovered that high-energy cosmic rays are not bombarding Earth equally from all directions, according to Astronomy Magazine. They found more cosmic rays coming from one particular region of space in a direction that falls outside the Milky Way's disk about 120 degrees from the galactic center.

After ruling out any possible sources for the high-energy cosmic rays inside the Milky Way, the researchers concluded that they must originate from outside the galaxy.

The Pierrre Auger Observatory detects cosmic rays indirectly with a huge array of more than 1,600 detectors spread across nearly 1,200 square miles (3,000 kilometers). As secondary particles from cosmic ray showers travel through tanks filled with pure water, the researchers analyzed the particles' arrival times and how they differed between various detectors. This allowed them to trace the particles up through the atmosphere and approximately identify their point of origin.

The limitations of the study meant it could not precisely pinpoint the location of the cosmic ray source. But astronomers are hopeful that ultimately they will find the origin of high energy cosmic rays and discover how they are generated.