Do cosmic rays that strike Earth come from outside Milky Way?

SCIENTISTS MAY BE ON VERGE OF SOLVING 50-YEAR-OLD RIDDLE

WASHINGTON DC: Ultrahigh-energy cosmic rays that occasionally hit the Earth may be coming from a distant source outside the Milky Way galaxy, a study suggests. Fifty years ago, scientists discovered that the Earth is occasionally hit by cosmic rays of enormous energies. Since then, they have argued about the source of those ultra-high-energy cosmic rays — whether they came from our galaxy or outside the Milky Way.

The answer lies in a galaxy or galaxies far, far away, according to a study published in the journal Science. Pierre Auger Collaboration, an internationally run observatory in Argentina, has been collecting data on such cosmic rays for a more than a decade. Researchers found that the rate of such cosmic particles, whose energies are a million times greater than that of the protons accelerated in the Large Hadron Collider (LHC), is about 6 per cent greater from one side of the sky than the other, in a direction where the distribution of galaxies is relatively high.

“We are now considerably closer to solving the mystery of where and how these extraordinary particles are created — a question of great interest to astrophysicists,” said Karlheinz Kampert, professor at University of Wuppertal in Germany. “Our observation provides compelling evidence that the sites of acceleration are outside the Milky Way,” said Kampert, spokesperson for the Auger Collaboration, which involves more than 400 scientists from 18 countries.