Calling them rays is a misnomer, based on decades-old misunderstanding of the phenomenon that identified it as electromagnetic radiation, but the name has stuck.
The study published in the journal Science demonstrated that those cosmic rays with energies a million times greater than that of the protons accelerated in the Large Hadron Collider - the world's largest and most powerful particle accelerator - come from much further away than from our own galaxy. This animation outlines the rays' journey to Earth from one possible starting point: being launched from a black hole at the center of a distant galaxy. The highest-energy cosmic rays only strike about once per square kilometre per year - equivalent to hitting the area of a soccer field about once per century. "The energy density in the extreme universe observed in cosmic rays, in neutrinos and gamma rays turns out to be the same", says Francis Halzen at the University of Wisconsin-Madison and the principal investigator of the IceCube Neutrino Observatory. And the best way we now have to identify their place of origin is to look at the direction they approach Earth from.
"Other possibilities include gamma ray bursts in other galaxies, which may accelerate cosmic rays".
Luckily, the tubs don't need to detect individual cosmic rays directly. The relative abundance changes with cosmic ray energy - the highest energy cosmic rays tend to be heavier nuclei.
When it comes back online, we'll start to get even closer to where exactly these cosmic rays are coming from.
Cosmic rays are tiny fragments of atoms, and they fill space with varying amounts of energies.
That is easier said than done, though. In 2007, an earlier study pointed to a correlation between active galactic nuclei and the arrival directions of the highest-energy cosmic rays then detected, but this correlation subsequently turned out to be not very significant. Scientists had previously speculated that the center of the Milky Way could be where these particles were originating, but the new study rules that out.
By studying more than 30,000 particles, the group discovered anisotropy; meaning the rate of cosmic ray arrivals is different, depending on which direction you look. The scientists found the most prominent arrival direction to be about 120 degrees away from the direction that points toward the center of the Milky Way.
"This result unequivocally establishes that ultra-high- energy cosmic rays are not just random wanderers of our nearby universe", said Paolo Privitera, professor at University of Chicago in the US.
Their conclusions were drawn using recordings from the Pierre Auger Observatory in Argentina, the largest cosmic ray observatory now in existence, and other data. Over 1,600 particle detectors over an area spanning 1,160 square miles collected information whenever a cosmic ray struck Earth, while telescopes would observe the light the charged particles emit. "These are some of the most important questions in astrophysics".
The cosmic rays that hit Earth may originate from beyond the Milky Way, according to a team of astronomers working at the Pierre Auger Observatory.
"We are now considerably closer to solving the mystery of where and how these extraordinary particles are created - a question of great interest to astrophysicists", said Karl- Heinz Kampert, professor at University of Wuppertal in Germany.
Cosmic rays reaching earth come from other galaxies far outside the Milky Way, new research has revealed.