Cosmic rays are high-energy particles which arrive from space. Lower energy particles are known to make up the solar wind, originating from the sun. While their higher energy counterparts have been observed for decades, their ultimate source has remained unknown.
An international group of scientists working with the Pierre Auger Observatory in Argentina has followed thousands of such high-energy cosmic rays. They found that the arrival direction of these particles indicates that they originate in other galaxies, as they are likely coming from outside of our own Milky Way.
The Extragalactic High Energy Cosmic Rays
The Pierre Auger Observatory, with its 1600 particle detectors spread over 1160 square miles, was specifically built to study cosmic rays hitting Earth and to investigate their source. The current research is the result of twelve years of observations.
Scientists hope that untangling the origins of these particles will teach us more about the Big Bang. Or about galaxy formation and the origins of the universe itself. Determining the source and direction of these particles is challenging. Because they are charged, they can be deflected by magnetic fields as they travel through the Milky Way or other galaxies.
The results, recently published in the journal Science, demonstrate that more particles are hitting Earth from a region of the sky about 120 degrees away from the center of the Milky Way galaxy.
Particles this energetic must have come from extremely violent astrophysical phenomena, say the researchers. Some galaxies have a massive black hole at their center, and some theorize that these could be the source of such high energy particles.
With this evidence that the source is outside our galaxy, scientists believe they are now getting closer to figuring out the mystery of how and where these particles are created. Particles of even higher energy, while rarer, are also known, and will be the subject of future studies.
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