High energy cosmic rays whose origins have been a mystery for 50 years come from beyond our galaxy, the Milky Way, scientists have confirmed. The powerful rays, consisting of energetic sub-atomic particles, may be born from cataclysmic violent events millions of light years away, evidence suggests.
The discovery reported in the journal Science follows 12 years of data collection by the Pierre Auger Observatory in Argentina.
The observatory has 1,600 particle detectors spread in a hexagonal grid over 1,160 square miles. Lead scientist Professor Gregory Snow, from the University of Nebraska-Lincoln in the US, said:
“There have been other pieces of evidence, but I would say this paper really confirms that most of the highest energy cosmic ray particles are not coming from the Milky Way galaxy. The sun emits low-energy cosmic ray particles that are detected here on Earth, but they are nowhere near as high energy as the particles detected at the Auger Observatory.
The particles we detect are so energetic they have to come from astrophysical phenomena that are extremely violent. Some galaxies have an explosive, massive black hole in their centres and there are theories that these very violent centres accelerate particles of very high energy that eventually reach Earth.”
Sky Map Showing the Cosmic Ray Flux
The evidence showed that high energy cosmic rays do not arrive from a direction pointing to the centre of the Milky Way, where some scientists had theorised they may originate.