They reveal a mystery: the origin of the cosmic rays

Almost a century after the German physicist Victor Hess – mounted in a balloon flying 5000 meters high – detected a “penetrating radiation” coming from space, and 65 years since Argentine physicists Horacio Ghielmetti, Emma Pérez Ferreira and Juan Roederer, among others, tried to build an observatory to study them in the Cordillera, a team of 400 scientists from 90 institutions and 16 countries (in which a group of Argentines plays a leading role) managed to answer one of the long-standing questions that pose these mysterious entities.
Lightning comes from outside the Milky Way.
In a paper published today in Science, they confirm that cosmic rays originate outside our galaxy.

“We are very happy,” says Mendoza astronomer Beatriz García, deputy director of the Institute of Technology and Detection of Astropartículas, and researcher of the Conicet.- The difference between this publication and another of 2007, where we already proposed an extragalactic origin, is the “degree of confidence “: that time we had reached what the physicists know as” 2.5 sigmas “, but now we come to” 5,6 sigmas. “The certainty that this is not a random data is very high. ”

The researchers came to this conclusion after analyzing records collected over 12 years by the Pierre Auger Observatory in Malargue, the largest experimental facility in the world, recording the passage of these particles with its network of 1600 detectors distributed in 3000 km2 (one surface 15 times larger than the city of Buenos Aires) and with 24 telescopes designed to record the fluorescence they emit.

Cosmic rays are protons and atomic nuclei that traverse the universe at a speed close to that of light. When they collide with the Earth’s atmosphere they unleash a cascade of secondary particles that can spread over 40 km2 or more. Although they were known for over half a century, their origin and mechanism of production remain a mystery. Between January 2004 and August 2016, Pierre Auger’s sensors detected thousands of ultra-high energy cosmic rays arriving from certain directions.

“Observations indicate that the flow of cosmic rays of very high energies is 6% higher in one-half of the sky than in the other,” says Conicet physicist Esteban Roulet, also the author of the paper, in a statement from the Balseiro Institute.

According to the scientist, the fact that greater flow is seen in one-half of the sky indicates that the effect of the magnetic field is important.

“Cosmic rays are the most energetic particles that are known and it is not known how they were accelerated and how they traveled to Earth,” adds Silvia Mollerach, the researcher at Conicet and another author who signed the research.

“They come from an area where there is a concentration of galaxies,” García explains, “but we do not know what they are, only they are within a radius of up to 100 megaparsecs, a distance equivalent to about 326 million light years.”

From now on, scientists estimate that they will need ten more years of observations to determine with a high degree of confidence what kind of particles they are.

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