![]() So discovering exactly where the more energetic cosmic rays come from has been a grail of physics since their discovery. ![]() In short, there is no straight path back to a source such as a photon of starlight provides astronomers, notes UW-Madison physics professor Justin Vandenbroucke. Positrons, muons, pions, kaons and more were sorted out of the subatomic clutter beginning in the 1930s, adding to a growing zoo of particles.īut finding out where cosmic rays originate is a more difficult task, because as the charged particles transit space, their trajectories are scrambled by the powerful magnetic fields that litter interstellar and intergalactic space. The particles raining down on Earth from cosmic ray events, and science’s growing ability to detect and parse the variety of secondary particles in the showers, led to a string of important discoveries. ![]() Until humans built the first particle accelerators in the 1950s, cosmic rays were the only way to study particles smaller than atoms. When cosmic rays arrive at Earth, they can collide with the nuclei of atoms in the atmosphere, creating a shower of billions of secondary particles. Helium and most other elements are also represented in the cosmic ray mix, but to a far lesser extent than hydrogen.īy the 1930s, cosmic rays had become an important window to the particles smaller than atoms. Most of the high-energy particles that come from space, scientists now know, are protons – the atomic nuclei of hydrogen, the most abundant element in the universe. At an altitude of more than 17,000 feet, Hess discovered that the rate of ionization was nearly four times greater than at ground level, demonstrating that the ions zipping through the air were of extraterrestrial origin.Īfter the discovery of cosmic radiation by Hess, a feat that would win him a Nobel Prize in 1936, the next questions for the new field of cosmic ray physics was, what are the particles made of, and how does nature make them? Where do they come from? That notion was dispelled in 1912, however, and the field of cosmic ray physics was born when the Austrian physicist Victor Hess, at great personal risk, carried devices known as electrometers high into the atmosphere in a free-floating hydrogen balloon to measure ionization rates at increasing heights. Austrian physicist Victor Hess in the balloon he used to determine that the energetic particles sensed in the air came from space.
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