The mystery of the origin of cosmic rays has been studied since their effects were detected for the first time, in the late 19th century. Recently, a few studies on some supernovae suggest that these dying stars are at least one of the sources of cosmic rays.
The supernova SN 1006 is very well known as in 1066 the explosion of that star was observed all over the world because it was much brighter than Venus and perhaps almost as much as the Moon. New observations using ESO’s Very Large Telescope (VLT) on what remains of the supernova suggests the presence of high-energy particles that may be the precursors of cosmic rays.
A team of astronomers led by Sladjana Nikolic of the Max Planck Institute for Astronomy in Heidelberg, Germany, used in particular the VIMOS (Visible Multi-Object Spectrograph), one of the VLT instruments, to examine what is left of the supernova SN 1006 in greater detail than ever.
The team’s purpose was to study what happens when high-speed material ejected by the supernova collides with the interstellar material. Observations show that there were many protons that moved at high speed in the gas in the shock front region.
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Almost simultaneously, there was the publication of the results of a study carried out using the Fermi gamma-ray space telescope about the supernovae IC 443 and W44. In particular, they used the Large Area Telescope (LAT), the Fermi instrument sensitive to gamma radiation in the range between 20 MeV and 300 GeV.
The Fermi space telescope allowed scientists to determine for the first time which particles are responsible for the emission of cosmic rays, identifying a type called the neutral pion. It’s a type of particle that has a very short life produced when cosmic ray protons hit normal protons. The pions decay quickly in a pair of gamma rays whose emissions show specific characteristics.
In 1949, it was the scientist Enrico Fermi to whom the Space Telescope is dedicated to propose the idea that the highest energy cosmic rays were accelerated in the magnetic fields of interstellar gas clouds. In the following decades, astronomers showed that supernova remnants were the best candidates for this process.
Over time, more and more powerful instruments were built and now it’s easier to find candidate of cosmic rays sources. However, this is a long process, the result of collaborations between different groups of scientists and agencies. For example, the investigation of the W44 supernova was helped by an observation made in 2011 by the Italian Space Agency’s gamma-ray observatory AGILE (Astrorivelatore Gamma ad Immagini LEggero).
The investigation of the cosmic rays sources isn’t just a scientific curiosity but has also a practical importance. In fact, those high-energy particles have effects on the equipment sent into space, and are probably to blame for the recent Mars Rover Curiosity computer problem. They can also penetrate the atmosphere and strike us, with serious effects because if they affect the DNA they can lead to mutations and diseases such as cancer.
