Cosmic Rays bombarding the Earth with ultra-high-energy extra-galactic radiation: it sounds like something out of science fiction or a global disaster blockbuster. But in fact Cosmic Rays, tiny particles with massive energy levels and speeds are constantly streaming into the Earth's atmosphere,
Luckily for us, our Earth's atmosphere and its magnetic field protect us from the harmful effects of these cosmic rays. These charged, sub-atomic particles (atomic nuclei, protons and electrons) collide with particles in the atmosphere and are fragmented into showers of much lower energy particles, which moslty evaporate before ever reaching the ground. The Earth's magnetic field channels a lot of the incoming particles towards the poles, where the infalling showers are visible as the beautiful flickering colours of the aurora, lighting up the night sky. Data from the Ice Cube observatory in Antarctica shows incoming cosmic rays spread all across the sky, except for a circular area shielded by the moon (see image at the bottom of the page).
Seeing the invisible
It's not necessary to be near the poles to detect cosmic rays showers though – they can also be detected by a specialised type of visible-light telescope known as a Cherenkov Telescope, which picks up the tiny flashes of radiation produced as the particles become fragmented. And radio telescopes such as 'LOFAR' in the Netherlands are now also being used to detect and find out more about these mysterious rays – astronomers hold high hopes for this technique as it can be used to collect data at any time, unlike Cherenkov telescopes which are limited to clear moonless nights.
Mysterious rays? Yes, because although their existence has been known about for over a century, very little is known about their origin – namely, where they come from and how they are accelerated to such high speeds. On their journey through space they are repeatedly pinged around and deflected by various magnetic fields which is why when they arrive at Earth they appear to come from all parts of the sky. This makes it virtually impossible to figure out the original direction from which they came. Current evidence suggests that they most likely come from outside the Milky Way, which doesn't narrow things down much!
Astronomers have however been able to identify what the particles are made of – just like most of the universe, the vast majority are hydrogen, with a significant proportion of helium, and trace amounts of other, heavier elements. And in 2013, research based on observations by the Fermi Gamma Ray Space Telescope found evidence that gamma ray emission (very high energy light waves) in two different supernovae was produced by cosmic ray collisions there. So it appears that at least some cosmic rays originate in these glowing remnants of exploded stars, but it's still unknow how they gain such high energy in the first place.
Whatever their origin, perhaps it is their practical effect on humankind that should concern us most. Thanks to our planet's atmosphere and magnetic field, as long as we stay on Earth they are not a threat to our health, but they present a major problem for space-based travel and technology. Astronauts travelling to the Moon or Mars for instance would receive dangerously high doses of radiation thanks to cosmic rays, and electronic equipment on spacecraft and satellites can malfunction when struck by them.
Humankind's exploration of space is likely to be severely restricted until we succeed in developing feasible methods to shield against the effect of these invisible but intensely powerful cosmic rays.
http://www.space.com/32644-cosmic-rays.html What are cosmic rays?
http://www.sciencemag.org/news/2016/03/mysterious-cosmic-rays-may-come-place-not-so-far-away Detection of Cosmic Rays using LOFAR
https://www.nasa.gov/mission_pages/GLAST/news/supernova-cosmic-rays.html#.V5IVCjUqSbc Cosmic rays in supernovae
http://www.nasa.gov/feature/goddard/real-martians-how-to-protect-astronauts-from-space-radiation-on-mars
1. Simon Swordy (U. Chicago), NASA
2.NASA/DOE/Fermi LAT Collaboration, NRAO/AUI, JPL-Caltech, ROSAT
3. IceCube Collaboration http://icecube.wisc.edu/news/view/131