The Earth is being bombarded from space at all hours. Fortunately, this bombardment is not the work of any ill-intentioned alien race and, in fact, we are not even aware of it in our day to day lives. The projectiles that rain on our planet are atomic nuclei that travel through space at speeds close to those of light that, if they are unlucky, end up crashing into our atmosphere.
We call these wandering particles cosmic rays. 90% of them are simple hydrogen nuclei (loose protons) that have been propelled at a very high speed by very energetic phenomena, such as supernovae. The rest are nuclei of heavier elements, mainly helium.
These particles usually have a kinetic energy between 10 mega electron-volts and 10 giga electron-volts, figures that are somewhere between picojoules and nanojoules. If you have not heard these units in your life, a 100 gram apple reaches 1 Joule of kinetic energy when falling from a height of one meter. In other words, cosmic rays usually carry an energy between a billion and a trillion times less than that of this especially small apple.
But every now and then, a record-breaking particle arrives on Earth: the so-called ultra-energetic cosmic rays, which have earned their reputation by striking the atmosphere with an energy that exceeds 10 billion giga electron-volts or , which is the same, 8 Joules.
In fact, the most energetic cosmic ray ever detected, the so -called “Oh-My-God particle” (in honor of the surprise that the astrophysicists who detected it took), had an energy of 48 Joules, comparable to that of a ball. baseball traveling 60 miles per hour. The truth is that it is difficult to assimilate this data: a simple proton with the energy of a macroscopic object.
We can detect and measure the energy of cosmic rays because, when they collide with the molecules of the different gases that make up the atmosphere, they undo them and produce a “cascade” of different particles. Although thanks to this it has been discovered that ultra-energetic cosmic rays tend to arrive from a specific sector of the sky, their origin is still uncertain. They are believed to form during gamma-ray bursts or when the shock wave produced by a hypernova, an explosion even more powerful than a supernova , propels the particles it runs into at tremendous speeds. Between 2004 and 2007 only 27 particles of this type were detected so, for now, we have no choice but to wait patiently to finish unraveling the mystery.
