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Cosmic rays and their origin – PhotoNick

By CoperNick

 Alice Gaggero

 

December 10, 2018

Everyone knows what it feels like to be out on a rainy day without an umbrella, but only few of us are aware that we are constantly showered by millions of imperceptible particles from outer space. These are known as Cosmic Rays.

A representation of the “rain” of particles, from Flickr

If we were to visualize Cosmic Rays, we could use “Solar Wind” – a type of low energy Cosmic Ray – as an example. Now I imagine you will be wondering how we can detect the presence of these rays without seeing or perceiving them.

The study of Cosmic Rays began with Victor Hess and his balloon flight in the August of 1912. Victor Hess was an Austrian physicist with a passion for radioactivity, a phenomenon which had been recently discovered at the time. Hess wanted to prove that terrestrial rocks produce an ionizing radiation. However, his experiments showed that the radiation increased with increasing height above sea level. This meant that the radiation wasn’t produced in the lithosphere and therefore had to come from outer space. Since then Physicists and Astrophysicists have been trying to understand where these particles come from and what generates them.

But why are we so interested in these particles? The answer is simple: human curiosity and the fact that this is the highest energy radiation found in nature. Today we can detect the ‘products’ of Cosmic Rays, muons and neutrinos, particles which are produced when Cosmic Rays collide with the atmosphere. This is the purpose of the IceCube detector located in the South Pole.

A photo of IceCube, from Flickr

But what are the components of Cosmic Rays? Cosmic Rays are made up of protons. They are classified according to their energy and place of origin. The energy of Cosmic Rays ranges between 107eV to 1020eV, with fewer rays having higher energy.

Cosmic Rays, from Flickr.

There are four types of Cosmic Rays:

  • Anomalous Cosmic Rays: these are the lowest energy type, with their energy varying between 107eV and 108eV. They are thought to originate from interstellar atoms, which are ionized by solar radiation and then accelerated by solar wind.
  • Solar Cosmic Rays: these have relatively low energies and are the most common type of Cosmic Rays. Their energy ranges between 107eV and 1010eV. Their name tells us where they come from: indeed they are produced in the solar corona during its flares and mass ejection.
  • Galactic Cosmic Rays: these have energies between 1010eV and 1015eV. They probably originated from supernova remnants. They are peculiar because they are detected isotropically, which means that they are equally distributed in all directions. They are different from the previous type of Cosmic Rays because they are rich in heavy elements, lithium, beryllium and boron. These rays can persist in space for thousands of years.
  • Ultra-high Energy Cosmic Rays: like their name suggests, these are the highest energy Cosmic Rays. The highest recorded energy for such a particle is 31020eV, about the same as a baseball thrown at 160 km/h! These are very rare and their origin remains a matter of dispute: a massive black hole; an active galactic nucleus; galaxy collisions etc.

Even today a lot remains unknown about Cosmic Rays: is there a limit to the energy of cosmic Rays and if so what is it? Where do they come from?

These are only a few of the questions that scientists are trying to answer. And remember: it is always raining upon planet Earth.

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