After having suspected it for more than a decade, for the first time, scientists have found evidence that the most energetic particles are generated outside the Milky Way . Those responsible for this discovery have been the astronomers of the Pierre Auger Observatory, in Argentina, who feel very satisfied to have verified the hypothesis.
Although the study has not been able to identify the specific sources of cosmic rays or how they reach such high energy levels, the analyzes carried out over a period of twelve years “have finally revealed that particles with the upper ranges of energy has an extragalactic origin “, explains Alan Watson, founding astronomer of the observatory.
Cosmic rays are made up of protons and other particles , whose nuclei can be as heavy as iron, charged that rain on the Earth’s atmosphere and collide with atomic nuclei in the air, producing an explosion formed by subatomic particles, which in turn collide with other nuclei . This generates a kind of invisible rain – known as cosmic rain or extensive atmospheric waterfall – that falls on an extension of the earth’s surface of thousands of square kilometers, which explains why the observatory is so large: the larger, the more particles are they capture.
To carry out the study, the Pierre Auger Observatory has installed 1,600 water tanks the size of a car every 1.5 kilometers, covering a total of 3,000 square kilometers in Mendoza, Argentina. In addition, it has twenty-four telescopes grouped into four groups that detect the flashes of ultraviolet light generated during cosmic rains from 85% of the earth’s sphere.
The most energetic particles only arrive once a century
Of the cosmic rays detected so far by this center, awarded in 2013 with the Special Mention of the Konex Prize to the most relevant institutions of Science and Technology in Argentina, energies greater than 8 x 1,018 electron volts (eV) have been recorded in more than thirty thousand particles. To get an idea of this extremely high energy power, scientists recall that the energy at which the Large Hadron Collider in Switzerland, the world’s most powerful particle accelerator, moves the protons is 7 x 1,012 eV. Although cosmic rays are generally very frequent, those with the highest energy are not so frequent. A 1,020 eV particle reaches one square kilometer from Earth only once every century, making it difficult to detect.
The results suggest that what was considered the main source of the highly energetic particles that reach Earth, a supermassive black hole in the center of the Milky Way, is not the origin of these cosmic rays, but rather they arrive from outside. In 2007, the observatory carried out a study that reached similar conclusions, although at that time the statistical data did not support them strongly enough. At this time, the researchers have ensured the robustness of the data. “I don’t think there is any doubt about the statistical significance of the latest results,” says astrophysicist Francis Halzen.
With the new data, the researchers hope to take the safe first steps about the origin of cosmic rays, one of the objectives for which the Pierre Auger Observatory was born. “This has been really big, a big surprise for me,” explains Halzen.
Highlight: The more energy a particle has, the more difficult it is to detect, so the observatory has an area of 3,000 square kilometers to capture as many as possible.
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