Galactic Explainer: A History of Cosmic Rays

by Jonathan Keathley

Victor Hess was born in Styria, Austria on June 24th, 1883. He conducted his undergraduate studies at the University of Graz, where he got his Bachelor’s in 1905 and his Ph.D. in physics in 1910.

Hess went on to discover cosmic rays in 1912 by using enhanced ion detectors invented just three years earlier.

Hess and colleagues launching a balloon for cosmic rays experiments.

During his experiments in 1912, Hess produced a series of 7 hydrogen balloon experiments to figure out if some of the high-energy particles he could detect from the surface of the Earth were not only coming from the radioactive elements in the Earth’s crust but were coming from space as well.

Each balloon had 3 instruments onboard, all of which were designed to detect various levels of radiation. Two of the instruments were shielded so that only high-energy particles could pass through, and the rest would be blocked. The last was left open to detect any particles that would hit the sensors.

The result of these 7 balloon flights was very surprising during this time.

Hess discovered that as you get higher up in the atmosphere the level of radiation or high-energy particles you encounter increases significantly. Indicating that the earth is being bombarded by tiny high-energy particles that contribute to the radiation detected on the surface. After this experiment was conducted between 1911 and 1912, it took another 24 years before Victor Hess won the Nobel Prize in 1936 for cosmic ray discovery.

These mysterious particles are still studied throughout the world today and many scientists are working to understand the mysteries be hide their origins.

The mystery of cosmic rays is not the rays themselves. Scientists understand what the rays consist of but the real uncertainty is how they are created.

Trying to figure out what objects in the universe can produce particles with such high energies/speeds has baffled scientists for years. Cosmic rays are little charged particles such as protons (hydrogen nuclei), electrons, and sometimes even large nuclei of different elements going extremely fast through the universe. These particles are traveling at speeds near the speed of light — meaning that somewhere in the universe an astronomical amount of energy was required to accelerate these particles to such high speeds.

Not all cosmic rays have a very well-known origin but for lower energy cosmic rays it is thought that they are produced by supernova remnants and their shock waves acting as particle accelerators causing these ionized particles to get to such high energy levels.

However, the highest energy cosmic rays are still not fully understood. Some scientists think that they come from the jets coming off active black holes but uncertainty remains.

As technology continues to get better, more cosmic ray sources are being discovered. The known energy range has also greatly increased which has led to more questions to be answered. With the ability to analyze these sources more thoroughly than ever before, it is only a matter of time before another breakthrough is made in the realm of cosmic rays.