Hola! I'm Alexa Guido, a young and curious woman passionate about science. Join me on an exciting journey to explore the wonders of the universe through the lens of physics.
Cosmic rays were named for the very first time in 1925 by Robert Milikan from UChicago, who mentioned them in a paper in the Science journal. The name is cool but although they are called cosmic rays, actually they are particles that rise from our Sun, supernovae, or black holes.
In fact, they are the nuclei of atoms with incredible energy that come from outer space. It may not seem like it, but the journey of these rays is chaotic because of their electric charge which makes them change their direction randomly when they travel through different magnetic fields.
Our planet receives trillions and trillions of these rays each day, but our atmosphere protects us from them, so you do not have to worry about it. However, the particles that get through it, we can track and study them. The cosmic rays have helped us since the 20th Century to discover antimatter and muons, which was the first evidence of subatomic particles beyond protons, neutrons, and electrons. Additionally, they can reveal to us the chemical and physical composition of the universe and what happens around supermassive black holes.
Today, we have various ways to detect cosmic rays, directly or via instruments, such as at the Pierre Auger Observatory in Argentina, where there is a gigantic water tank that catches signals when cosmic rays hit it and a UV detector that traps them. Or the Large High Altitude Air Shower Observatory in China, which collects showers of cosmic rays and gamma rays from space. Nevertheless, using balloons is also popular, as scientists send detectors aboard these balloons to high altitudes and record detections.
Almost 100 years after their naming, we know that about 90% of cosmic rays are composed of hydrogen, 9% helium, and 1% are heavier elements like iron. A mystery is their energies, we know that the energy of each particle depends on its mass and how fast it reaches the detectors. However, this energy can be as small as you can imagine to hundreds of millions of times more energetic than the particle collisions we create in colliders. Many questions like these tie cosmic-ray astrophysics to basic particle physics and the fundamental nature of the universe.
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